Classification of Additives for Organic Photovoltaic Devices - Machui, Florian; Maisch, Philipp; Burgues-Ceballos, Ignasi; Langner, Stefan; Krantz, Johannes; Ameri, Tayebeh; Brabec, Christoph (ChemPhysChem, 2015)
The use of additives to improve the performance of organic photovoltaic cells has been intensely researched in recent years. However, so far, no system has been reported for the classification of additives and their functions. In this report, a system for classifying additives according to the fundamental mechanism by which they influence microstructure formation for P3HT:PCBM is suggested. The major parameters used for their classification are solubility and drying kinetics. Both are discussed in detail and their consequences on processing are analyzed. Furthermore, a general mechanism to classify the impact of additives on structure formation is suggested and discussed for different materials relevant to organic photovoltaic devices.
Keywords: additives; fullerenes; ink formulation; organic photovoltaics; polymers

Closing the loop: recycling of MAPbI3 perovskite solar cells - Wu, Zhenni; Sytnyk, Mykhailo; Zhang, Jiyun; Babayeva, Gülüsüm; Kupfer, Christian; Hu, Jin; Arnold, Simon; Hauch, Jens; Brabec, Christoph; Peters, Ian Marius (Energy and Environmental Science, 2024)
Closed-loop recycling is crucial in the rapidly expanding era of photovoltaic deployment. Yet, the recycling of commercial silicon photovoltaic modules presents challenges due to laborious component separation. In contrast, layers in solution-processed solar cells can be separated with relative ease through selective dissolution. In this study, we report on the recovery of every layer in a planar MAPbI3 perovskite solar cell using a layer-by-layer solvent extraction approach, followed by purification or modification to restore quality. This method potentially allows for up to 99.97% recycled mass, thereby conserving resources and reducing waste. We assessed material quality by substituting each fresh material with its recycled equivalent during solar cell production. Subsequently, solar cells were fabricated with either several or all layers comprising recycled materials. Every combination yielded efficiency comparable to cells constructed exclusively with fresh materials, demonstrating the efficacy of the developed recycling process. Our mass and value analysis highlights ITO glass has the highest recycling priority and the need for circular utilization for by-product chemicals, especially cleaning agents. Techno-economic projections suggest that the proposed recycling procedure has the potential to afford substantial cost savings. In the lab, recycling could reduce material costs by up to 63.7%, in industrial manufacturing by up to 61.4%. A life cycle assessment reveals this recycling method can reduce environmental impacts.
CRIS-Team Scopus Importer:2024-06-07

CO2 snow jet cleaning as a roll-to-roll compatible method for deburring IMI substrates after laser patterning - Wagner, Michael; Distler, Andreas; Schmidt, Hans-Dieter; Classen, A.; Stubhan, T.; Koegl, M.; Illg, J.; Brabec, Christoph; Egelhaaf, Hans-Joachim (Flexible and Printed Electronics, 2023)
Burring is commonly encountered upon patterning of dielectric-metal-dielectric (DMD) transparent electrodes by laser ablation. These burrs are conductive and thus lead to shunting of the (opto-)electronic devices built upon these electrodes. In this work, CO2 snow jet blasting is presented as a convenient and reliable method for deburring laser-patterned DMD electrodes during roll-to-roll manufacturing of organic solar modules. As CO2 snow jet blasting significantly reduces the extent of shunting and concomitantly avoids scratching the electrode, the photoelectrical conversion efficiencies of the solar modules thus produced are higher than those obtained for traditional deburring techniques.
CRIS-Team Scopus Importer:2023-02-10
Keywords: carbon dioxide snow jet; deburring; laser patterning; printed photovoltaics; transparent electrode

Coloring Semitransparent Perovskite Solar Cells via Dielectric Mirrors - Ramírez Quiroz, César Omar; Bronnbauer, Carina; Levchuk, Ievgen; Hou, Yi; Brabec, Christoph; Forberich, Karen (ACS nano, 2016)
While perovskite-based semitransparent solar cells for window applications show competitive levels of transparency and efficiency compared to organic photovoltaics, the color perception of the perovskite films is highly restricted because band gap engineering results in losses in power conversion efficiencies. To overcome the limitation in visual aesthetics, we combined semitransparent perovskite solar cells with dielectric mirrors. This approach enables one to tailor the device appearance to almost any desired color and simultaneously offers additional light harvesting for the solar cell. In the present work, opto-electrical effects are investigated through quantum efficiency and UV-to-visible spectroscopic measurements. Likewise, a detailed chromaticity analysis, featuring the transmissive and reflective color perception of the device including the mirror, from both sides and in different illumination conditions, is presented and analyzed. Photocurrent density enhancement of up to 21% along with overall device transparency values of up to 31% (4.2% efficiency) is demonstrated for cells showing a colored aesthetic appeal. Finally, a series of simulations emulating the device chromaticity, transparency, and increased photocurrent density as a function of the photoactive layer thickness and the design wavelength of the dielectric mirror are presented. Our simulations and their experimental validation enabled us to establish the design rules that consider the color efficiency/transparency interplay for real applications.
Keywords: Bragg mirror; dielectric mirror; perovskite photovoltaics; room temperature crystallization; semitransparent

Combinatorial screening of polymer: Fullerene blends for organic solar cells by inkjet printing - Teichler, Anke; Eckardt, Rebecca; Hoeppener, Stephanie; Friebe, Christian; Perelaer, Jolke; Senes, Alessia; Morana, Mauro; Brabec, Christoph; Schubert, Ulrich S. (Advanced Energy Materials, 2011)
Polymer: fullerene blends were screened in a combinatorial approach using inkjet printing thin film libraries for photovoltaic devices. The application of inkjet printing enabled a fast and simple experimental workflow from film preparation to the study of structure-property-relationships with a very high material efficiency. Inkjet printing requires less material for the preparation of thin film libraries in comparison to other dispensing techniques, like spin-coating. Two polymers (PCPDTBT, PSBTBT) and two fullerene derivatives (mono-PCBM, bis-PCBM) were investigated in various blend ratios, concentrations, solvent ratios, and film thicknesses. Morphological and optical properties of the inkjet printed films were investigated and compared with spin-coated films. This study shows the principle of an experimental setup from solution preparation to film characterization for the combinatorial investigation of large polymer: fullerene libraries. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: Blend ratios; Combinatorial approach; Combinatorial screenings; Experimental setup; Film characterizations; Fullerene derivative; Material efficiency; Organic solar cell; Photovoltaic devices; Spin-coated films; Thin film libraries Engineering controlled terms: Fullerenes; Ink jet printing; Libraries; Optical properties; Polymer blends; Polymers; Thin films Engineering main heading: Film preparation

Combined Computational Approach Based on Density Functional Theory and Artificial Neural Networks for Predicting the Solubility Parameters of Fullerenes - Perea Ospina, Jose Dario; Langner, Stefan; Salvador, Michael Filipe; Kontos, Janos; Jarvas, Gabor; Winkler, Florian; Machui, Florian; Görling, Andreas; Dallos, Andras; Ameri, Tayebeh; Brabec, Christoph (Journal of Physical Chemistry B, 2016)
The solubility of organic semiconductors in environmentally benign solvents is an important prerequisite for the widespread adoption of organic electronic appliances. Solubility can be determined by considering the cohesive forces in a liquid via Hansen solubility parameters (HSP). We report a numerical approach to determine the HSP of fullerenes using a mathematical tool based on artificial neural networks (ANN). ANN transforms the molecular surface charge density distribution (σ-profile) as determined by density functional theory (DFT) calculations within the framework of a continuum solvation model into solubility parameters. We validate our model with experimentally determined HSP of the fullerenes C, PCBM, bisPCBM, ICMA, ICBA, and PCBM and through comparison with previously reported molecular dynamics calculations. Most excitingly, the ANN is able to correctly predict the dispersive contributions to the solubility parameters of the fullerenes although no explicit information on the van der Waals forces is present in the σ-profile. The presented theoretical DFT calculation in combination with the ANN mathematical tool can be easily extended to other π-conjugated, electronic material classes and offers a fast and reliable toolbox for future pathways that may include the design of green ink formulations for solution-processed optoelectronic devices.
Keywords: Engineering controlled terms: Computation theory; Design for testability; Fullerenes; Molecular dynamics; Neural networks; Optoelectronic devices; Solubility; Van der Waals forces Computational approach; Continuum solvation models; Electronic materials; Environmentally benign; Hansen solubility parameters; Molecular dynamics calculation; Numerical approaches; Solubility parameters Engineering main heading: Density functional theory

Combining unsupervised and supervised learning in microscopy enables defect analysis of a full 4H-SiC wafer - Nguyen, Binh Duong; Steiner, Johannes; Wellmann, Peter; Sandfeld, Stefan (MRS Communications, 2024)
Detecting and analyzing various defect types in semiconductor materials is an important prerequisite for understanding the underlying mechanisms and tailoring the production processes. Analysis of microscopy images that reveal defects typically requires image analysis tasks such as segmentation and object detection. With the permanently increasing amount of data from experiments, handling these tasks manually becomes more and more impossible. In this work, we combine various image analysis and data mining techniques to create a robust and accurate, automated image analysis pipeline for extracting the type and position of all defects in a microscopy image of a KOH-etched 4H-SiC wafer. Graphical abstract: (Figure presented.)
CRIS-Team Scopus Importer:2025-02-04
Keywords: Dislocations; Machine learning

Combustion of solid fuel in a hybrid porous reactor - Jovicic, Vojislav; Fedorova, Nataliia; Zbogar-Rasic, Ana; Makongue Nloka, Daniel Ernest Gustave; Reichert, Fernando; Delgado, Antonio (Energy Procedia, 2017)
One of the most significant human-made methane emission sources is the municipal solid waste (MSW), deposited on sanitary landfills and open dumps [1,2]. Within this work, an alternative MSW treatment concept is presented, which could provide a relatively clean waste/biomass-to-energy transformation. The proposed procedure comprises of a combustion and a gasification (or pyrolysis) step, which are consecutively taking place in a two-stage hybrid porous reactor system. The core of the system are two packed bed reactors, in which solid fuel (waste or biomass) is mixed with inert ceramic particles of similar size. This paper overviews the initial experimental investigation of the combustion step of a hybrid mixture, composed of wood pellets (fuel) and alumina balls (inert ceramic particles) in a 250 mm-high batch reactor. The temperature profile along the reactor, the concentration of CO and the flame front propagation velocity were measured as a function of the ceramic particle size (11 and 20 mm), the inert-to-fuel mass ratio (0:1, 2:1, 3:1) and the airflow rate (30, 42, 60 l/min). Experiments indicate that an increase of the mass ratio of inert-to-fuel material and a decrease of the inert ceramic particles size lead to a decrease of the maximum temperature of the packed hybrid bed. Measured CO concentrations showed strong dependence on the inert ceramic particle size, i.e. the particle size reduction from 20 to 11 mm resulted in a significant reduction of CO-emission peaks. The maximum flame front propagation velocity of 0.2 mm/sec was detected for the airflow of 42 l/min, the particle size of 20 mm and the mass ratio of 3:1.
UnivIS-Import:2018-09-11:Pub.2017.tech.ITC.stmmec.combus
Keywords: allothermal gasification; Combustion; hybrid filtration combustion; MSW; packed bed

Comparative analysis of outdoor energy harvest of organic and silicon solar modules for applications in BIPV systems - Feroze, Sarmad; Distler, Andreas; Forberich, Karen; Ahmed Channa, Iftikhar; Doll, Bernd; Brabec, Christoph; Egelhaaf, Hans-Joachim (Solar Energy, 2023)
Organic photovoltaics (OPV) have the potential to fill niches that traditional silicon photovoltaics (Si-PV) have left open so far. Building-integrated photovoltaics (BIPV) is one key area where OPV modules can play a vital role due to their functional attributes of semitransparency, flexibility, and lightweight. However, the architectural constraints and physical layout of buildings often do not allow the installation of photovoltaic (PV) modules at their optimal angles. Herein, we report the outdoor energy harvest of commercial OPV, and monocrystalline silicon (m-Si) modules mounted at inclinations of 45° and 90°, using the ISOS-O2 protocol as a test standard. The semitransparent OPV modules incorporating a P3HT:PCBM bulk heterojunction absorbing layer were found to offer daily specific energy yields (YF) that are 10–15% higher than those of the m-Si modules at 45° inclination. For vertical (90°) mounting, the YF of the OPV modules is even 24–30% higher than that of their inorganic counterparts, thus making them ideally suited for façade integrated BIPV. Laboratory investigations reveal that the superior performance of OPV modules in the vertical position is mainly due to a strongly enhanced fill factor (FF) at reduced in-plane irradiance. At a 45° inclination, the positive temperature coefficient of the OPV modules also plays an important role during high-irradiance hours.
CRIS-Team Scopus Importer:2023-09-22
Keywords: Building-integrated photovoltaics; Energy harvest; Organic photovoltaics; Outdoor monitoring

Comparative study of the luminescence of Al2O3:C and Al2O3 crystals under synchrotron radiation excitation - Zorenko, Yu.; Fabisiak, Kazimierz; Zorenko, T.; Mandowski, Arkadiusz; Xia, Qi; Batentschuk, Miroslaw; Friedrich, Jochen; Zhusupkalieva, G. (Journal of Luminescence, 2013)
The work is related to studying the luminescence of F and F+ centers and excitons localized around F-like centers in Al2O3 host based on the results of the comparative investigation of the luminescent properties of Al2O3 and Al2O3:C crystals under excitation by synchrotron radiation in the 3.7–15 eV rang
Keywords: Al2O3 and Al2O3:C crystals; Luminescence; Oxygen vacancy; Excitons; F and F+ centers

Comparison of achievable contrast features in computed tomography observing the growth of a 4H-SiC bulk crystal - Salamon, Michael; Arzig, Matthias; Wellmann, Peter; Uhlmann, Norman (Materials, 2019)
Today the physical vapor transport process is regularly applied for the growth of bulk SiC crystals. Due to the required high temperature of up to 2400 °C, and low gas pressure of several Mbar inside the crucible, the systems are encapsulated by several layers for heating, cooling and isolation inhibiting the operator from observing the growth. Also, the crucible itself is fully encapsulated to avoid impurities from being inserted into the crystal or disturbing the temperature field distribution. Thus, once the crucible has been set up with SiC powder and the seed crystal, the visible access to the progress of growth is limited. In the past, X-ray radiography has allowed this limitation to be overcome by placing the crucible in between an X-ray source and a radiographic film. Recently these two-dimensional attenuation signals have been extended to three-dimensional density distribution by the technique of computed tomography (CT). Beside the classic X-ray attenuation signal dominated by photoelectric effect, Compton effect and Rayleigh scattering, X-ray diffraction resulting in the crystalline structure of the 4H-SiC superimposes the reconstructed result. In this contribution, the achievable material contrast related to the level of X-ray energy and the absorption effects is analyzed using different CT systems with energies from 125 kV to 9 MeV. Furthermore the X-ray diffraction influence is shown by the comparison between the advanced helical-CT method and the classical 3D-CT.
CRIS-Team Scopus Importer:2019-12-10
Keywords: 3D in situ analysis; Bragg diffraction; Computed tomography; Helical-CT; PVT growth process surveillance

Comparison of different sources for laboratory X-ray microscopy - Ebensperger, T.; Stahlhut, P.; Nachtrab, Frank; Zabler, S.; Hanke, Randolf (Journal of Instrumentation, 2012)
This paper describes the setup of two different solutions for laboratory X-ray microscopy working with geometric magnification. One setup uses thin-film transmission targets with an optimized tungsten-layer thickness and the electron gun and optics of an electron probe micro analyzer to generate a very small X-ray source. The other setup is based on a scanning electron microscope and uses microstructured reflection targets. We also describe the structuring process for these targets. In both cases we show that resolutions of 100 nm can be achieved. Also the possibilities of computed tomography for 3D imaging are explored and we show first imaging examples of high-absorption as well as low-absorption specimens to demonstrate the capabilities of the setups.
EAM Import::2019-03-13

Comparison of Drone-based IR-imaging with Module Resolved Monitoring Power Data - Teubner, Janine; Kruse, Ingmar; Scheuerpflug, Hans; Buerhop-Lutz, Claudia; Hauch, Jens; Camus, Christian; Brabec, Christoph (Energy Procedia, 2017)
Two testing methods for photovoltaic (PV) plants, an infrared (IR)-measurement aerial system and a monitoring system on module level, are compared with respect to their capabilities for identifying irregularities of PV panels in a PV plant. For the first method, a hypothesis is tested that infrared temperature and module power can be correlated with an empirical linear correlation using the raw measurement data of the second method. A workaround is proposed how to quantify power losses for unknown PV plants showing at the same time how power losses depend on ambient conditions. Also, the data is used to improve results from the IR-measurements. The second method is explained to compare the two methods. It is shown that each method offers different advantages, helping to properly assess and schedule O&M measures.
Keywords: Engineering controlled terms: DronesElectric lossesFlight dynamicsInfrared imagingInspectionPhotovoltaic cellsReliabilitySiliconTestingThermography (imaging)Unmanned aerial vehicles (UAV) Compendex keywords Ambient conditionsInfrared measurementsIR thermographyLinear correlationMonitoring systemPhotovoltaicsPower-lossesRaw measurements Engineering main heading: Monitoring

Comparison of electroluminescence intensity and photocurrent of polymer based solar cells - Hoyer, Ulrich; Pinna, Luigi; Swonke, Thomas; Auer, Richard; Brabec, Christoph; Stubhan, Tobias; Li, Ning (Advanced Energy Materials, 2011)
The reciprocity theorem for solar cell predicts a linear relation between electroluminescence emission and photovoltaic quantum efficiency and an exponential dependence of the electroluminescence signal on the applied voltage. Both dependencies are experimentally verified for polymer based solar cells in this paper. Furthermore it is shown, that electroluminescence imaging of organic solar cells has the potential to visualize the photocurrent distribution significantly faster than standard laser beam induced current mapping (LBIC) techniques.

Comparison of the sputtered TiO2 anatase and rutile thin films as electron transporting layers in perovskite solar cells - Shahvaranfard, Fahimeh; Li, Ning; Hosseinpour, Saman; Hejazi, Seyedsina; Zhang, Kaicheng; Altomare, Marco; Schmuki, Patrik; Brabec, Christoph (Nano Select, 2021)
We examine comparatively the performance of sputtered TiO2 rutile and anatase thin films as an electron transport layer (ETL) inMAPbI3-based perovskite solar cells. Both anatase and rutile TiO2 ETLs are deposited (on fluorine-doped tin oxide [FTO] substrates) by magnetron sputtering in the form of nanocrystalline thin films. We systematically investigate the role of crystallographic phase composition of TiO2 ETLs on the photovoltaic performance of perovskite solar cells. The champion power conversion efficiencies (PCEs) of 18.4% and 17.7% under reverse scan mode are obtained for perovskite solar cells based on TiO2 anatase and TiO2 rutile ETL, respectively. The results show that the magnetron sputtering deposited ETLs differ from each other only in their phase composition while the overall performance of the devices is not greatly affected by the crystallographic phase of the TiO2 ETLs. Our results point to an important fact that for a proper and reliable comparison between the performance of TiO2 anatase and rutile ETLs, it is crucial to investigate films of similar morphology and structure that are synthesize under similar condition
Keywords: magnetron sputtering; perovskite solar cell; TiO2 anatase; TiO2 rutile

Comparison of various sol-gel derived metal oxide layers for inverted organic solar cells - Oh, Hyunchul; Krantz, Johannes; Litzov, Ivan; Stubhan, Tobias; Pinna, Luigi; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2011)
Inverted bulk-heterojunction solar cells have recently captured high interest due to their environmental stability as well as compatibility to mass production. This has been enabled by the development of solution processable n-type semiconductors, mainly TiO and ZnO. However, the device performance is strongly correlated to the electronic properties of the interfacial materials, and here specifically to their work function, surface states as well as conductivity and mobility. It is noteworthy to say that these properties are massively determined by the crystallinity and stoichiometry of the metal oxides. In this study, we investigated aluminum-doped zinc oxide (AZO) as charge selective extraction layer for inverted BHJ solar cells. Thin AZO films were characterized with respect to their structural, optical and electrical properties. The performance of organic solar cells with an AZO electron extraction layer (EEL) is compared to the performance of intrinsic ZnO or TiO EELs. We determined the transmittance, absorbance, conductivity and optical band gap of all these different metal oxides. Furthermore, we also built the correlations between doping level of AZO and device performance, and between annealing temperature of AZO and device performance. © 2011 Elsevier B.V.
Keywords: Al doped ZnO (AZO); Charge selective extraction layer; Inverted Organic Solar cells; Sol-Gel synthesis; TiOx; ZnO

Composition-Dependent Optical Band Bowing, Vibrational, and Photochemical Behavior of Aqueous Glutathione-Capped (Cu, Ag)-In-S Quantum Dots - Raievska, Oleksandra; Stroyuk, Oleksandr; Azhniuk, Yuriy; Solonenko, Dmytro; Barabash, Anastasia; Brabec, Christoph; Zahn, Dietrich R. T. (Journal of Physical Chemistry C, 2020)
A mild aqueous synthesis of colloidal 2-4 nm (Cu, Ag)-In-S (CAIS) quantum dots (QDs) stabilized by surface metal complexes with glutathione was introduced. Linear variations of the interplanar distances as well as of the characteristic Ag(Cu)-S-related Raman vibrational frequencies of CAIS QDs with the increasing copper content show such QDs to be solid solutions rather than a mixture of AIS and CIS phases. At the same time, the band gaps and the energies of the photoluminescence (PL) band maxima of CAIS QDs show nonmonotonous changes decreasing from AIS to CAIS QDs (50 mol % Cu) and then increasing back for Cu-richer CAIS compositions and pure CIS. This behavior was interpreted as a result of the band bowing phenomenon. The bowing parameters of CAIS QDs determined from both absorption spectra (1.10 eV) and PL spectra (0.38 eV) are close to the range typically reported for ternary bulk MI-MIII-S compounds with the MI sites occupied by a mixture of copper and silver cations. The PL intensity of CAIS QDs was found to decrease during PL registration due to the photochemical decomposition of QDs, and the efficiency of this process increases with the increasing copper content. A similar trend was found in the photocatalytic reduction of methylviologen cations by hydrosulfide anions in the presence of CAIS. The initial rate of this reaction increased monotonously from AIS to CAIS to CIS QDs, with the activity of the CAIS QDs (50 mol % Cu) and pure CIS QDs being, respectively, 1.5 and 2.7 times higher than the photoactivity of pure AIS QDs. This trend is compliant with a strong decrease in the PL emission efficiency observed from AIS to CAIS to CIS QDs. Similar optical and photochemical properties were revealed for core/shell CAIS/ZnS QDs. The band bowing effect and photochemical activity of mixed CAIS (CAIS/ZnS) QDs open good perspectives for light-conversion applications in the photon energy range down to 1.8 eV.
CRIS-Team Scopus Importer:2020-10-23

Composition Engineering of All-Inorganic Perovskite Film for Efficient and Operationally Stable Solar Cells - Tian, Jingjing; Wang, Jing; Xue, Qifan; Niu, Tianqi; Yan, Lei; Zhu, Zonglong; Li, Ning; Brabec, Christoph; Yip, Hin Lap; Cao, Yong (Advanced Functional Materials, 2020)
Cesium-based inorganic perovskites have recently attracted great research focus due to their excellent optoelectronic properties and thermal stability. However, the operational instability of all-inorganic perovskites is still a main hindrance for the commercialization. Herein, a facile approach is reported to simultaneously enhance both the efficiency and long-term stability for all-inorganic CsPbI2.5Br0.5 perovskite solar cells via inducing excess lead iodide (PbI2) into the precursors. Comprehensive film and device characterizations are conducted to study the influences of excess PbI2 on the crystal quality, passivation effect, charge dynamics, and photovoltaic performance. It is found that excess PbI2 improves the crystallization process, producing high-quality CsPbI2.5Br0.5 films with enlarged grain sizes, enhanced crystal orientation, and unchanged phase composition. The residual PbI2 at the grain boundaries also provides a passivation effect, which improves the optoelectronic properties and charge collection property in optimized devices, leading to a power conversion efficiency up to 17.1% with a high open-circuit voltage of 1.25 V. More importantly, a remarkable long-term operational stability is also achieved for the optimized CsPbI2.5Br0.5 solar cells, with less than 24% degradation drop at the maximum power point under continuous illumination for 420 h.
CRIS-Team Scopus Importer:2020-06-09
Keywords: composition engineering; CsPbI; defect passivation; operationally stable; PbI

Comprehensive Investigation and Analysis of Bulk-Heterojunction Microstructure of High-Performance PCE11:PCBM Solar Cells - Zhang, Chaohong; Heumüller, Thomas; Gruber, Wolfgang; Almora, Osbel; Du, Xiaoyan; Ying, Lei; Chen, Junwu; Unruh, Tobias; Cao, Yong; Li, Ning; Brabec, Christoph (ACS Applied Materials and Interfaces, 2019)
Worldwide research efforts have been devoted to organic photovoltaics in the hope of a large-scale commercial application in the near future. To meet the industrial production requirements, organic photovoltaics that can reach power conversion efficiency (PCE) of over 10% along with promising operational device stability are of utmost interest. In the study, we take PCE11:PCBM as a model system, which can achieve over 11% PCE when processed from nonhalogen solvents, to deeply investigate the morphology− performance−stability correlation. We demonstrate that four batches of PCE11 with varying crystalline properties can achieve similar high performance in combination with PCBM. Careful device optimization is necessary in each case to properly address the requirements for the quite distinct microstructures. The bulk-heterojunction (BHJ) microstructure is comprehensively investigated as a function of the macromolecular weight and crystallinity. It is demonstrated that small differences in morphology significantly affect the kinetics and thermodynamic equilibrium of the BHJ microstructure as well as the photostability and thermal stability of the PCE11:PCBM solar cells<br
Keywords: in situ capacitance spectroscopy; organic photovoltaics; bulk-heterojunction microstructures; film morphology; PCE11:PCBM solar cells

Computational optimization and solution-processing of thick and efficient luminescent down-shifting layers for photovoltaics - Solodovnyk, Anastasiia; Kick, Christopher; Osvet, Andres; Egelhaaf, Hans-Joachim; Stern, Edda; Batentschuk, Miroslaw; Forberich, Karen; Brabec, Christoph (Physics, Simulation, and Photonic Engineering of Photovoltaic Devices V, 2016)
Luminescent down-shifting (LDS) is a simple, powerful tool for increasing the range of solar irradiance that can be efficiently utilized by photovoltaic devices. We developed an optical model to simulate the ideal optical properties (absorbance, transmittance, luminescence quantum yield, etc.) of LDS layers for solar cells. We evaluated which quantum efficiencies and which optical densities are necessary to achieve an improvement in solar cell performance. In particular we considered copper indium gallium diselenide (CIGS) devices. Our model relies on experimentally measured data for the transmission and emission spectra as well as for the external quantum efficiency (EQE) of the solar cell. By combining experimental work with this optical model, we aim to propose an environmentally friendly technology for coating thick (300-500 μm), efficient luminescent down-shifting layers. These layers consist of polyvinyl butyral (PVB) and organic UV-converting fluorescent dyes. The absorption coefficients and luminescence quantum yields of the dyes were determined both in a solution of the solvent benzyl alcohol and in the solid polymer layers. This data shows that the dyes retain luminescence quantum yields of approximately 90% after solution-processing. The produced layers were then applied to CIGS solar cells, thereby improving the EQE of the devices in the UV region. At a wavelength of 390 nm, for instance, the EQE increased from 18% to 53%. These values closely agree with the theoretically calculated ones. The proposed technology, thus, provides a pathway toward efficient, fully solutionprocessable encapsulated photovoltaic modules.
Keywords: Absorbance; EQE; Luminescence; Organic dye; Photovoltaics; Quantum yield

Computer vision tool for detection, mapping, and fault classification of photovoltaics modules in aerial IR videos - Bommes, Lukas; Pickel, Tobias; Buerhop-Lutz, Claudia; Hauch, Jens; Brabec, Christoph; Peters, Ian Marius (Progress in Photovoltaics, 2021)
Increasing deployment of photovoltaics (PV) plants demands for cheap and fast inspection. A viable tool for this task is thermographic imaging by unmanned aerial vehicles (UAV). In this work, we develop a computer vision tool for the semi-automatic extraction of PV modules from thermographic UAV videos. We use it to curate a dataset containing 4.3 million IR images of 107,842 PV modules from thermographic videos of seven different PV plants. To demonstrate its use for automated PV plant inspection, we train a ResNet-50 to classify ten common module anomalies with more than 90% test accuracy. Experiments show that our tool generalizes well to different PV plants. It successfully extracts PV modules from 512 out of 561 plant rows. Failures are mostly due to an inappropriate UAV trajectory and erroneous module segmentation. Including all manual steps our tool enables inspection of 3.5 MWp to 9 MWp of PV installations per day, potentially scaling to multi-gigawatt plants due to its parallel nature. While we present an effective method for automated PV plant inspection, we are also confident that our approach helps to meet the growing demand for large thermographic datasets for machine learning tasks, such as power prediction or unsupervised defect identification.
CRIS-Team WoS Importer:2021-07-16

Concentration and excitation effects on the exciton dynamics of poly(3-hexylthiophene)/PbS quantum dot blend films - Tsokkou, D.; Itskos, G.; Choulis, S.; Yarema, Maksym; Heiß, Wolfgang; Othonos, A. (Nanotechnology, 2013)
The dynamics of photoexcitations in hybrid blends of poly(3-hexylthiophene) (P3HT) conjugated polymer donor and oleic-acid capped lead sulfide (PbS) quantum dot (QD) acceptors of different concentrations-for light harvesting applications-were investigated using time-resolved transmission and photoluminescence spectroscopies. Following excitation at 400 nm and probing in the 500-1000 nm region, we find that geminate excitation recombination in the blend of P3HT/PbS QDs dominates the transient decays at sub-ns times while intermaterial interactions such as charge transfer processes appear at longer times in the 1-50 ns regime. For the hybrid blend films with lower QD concentrations (<67% wt), polymer exciton recombination dominates the overall transient absorption signal. For higher QD contents, QD state relaxation effects become visible. Excitation density studies reveal the presence of linear exciton relaxation effects in the P3HT region while carrier decay for films with high PbS QD concentration is influenced by QD Auger recombination. Time-resolved luminescence shows that electron transfer from the P3HT/PbS QDs appears relatively inefficient in comparison to the geminate recombination, while hole transfer competes favorably to intrinsic QD recombination.
Keywords: Auger recombination; Charge transfer process; Exciton relaxation; Geminate recombination; Poly-3-hexylthiophene; Time-resolved luminescence; Time-resolved transmission; Transient absorption

Conditions for the Invertibility of the Isoparametric Mapping for 3D Multilinear Finite Elements - Knabner, Peter; Korotov, Sergey; Summ, Gerhard (17th GAMM-Seminar Leipzig on Construction of Grid Generation Algorithms, 2001)

Conditions for the invertibility of the isoparametric mapping for hexahedral finite elements - Knabner, Peter; Korotov, Sergey; Summ, Gerhard (Finite Elements in Analysis and Design, 2003)
The conditions for the invertibility of the isoparametric mapping for hexahedral finite elements are discussed. The mapping gives a reference element onto a global element for trilinear finite elements. An algorithm that checks the positivity of the Jacobian determinant depending on the position of the vertices is also presente
Keywords: Hexahedral finite elements; Invertibility; Isoparametric mapping

Conductance Enhancement Mechanisms of Printable Nanoparticulate Indium Tin Oxide (ITO) Layers for Application in Organic Electronic Devices - Groß, Michael; Linse, Nicolas; Maksimenko, Ilja; Wellmann, Peter (Advanced Engineering Materials, 2009)
Keywords: ITO; nanoparticultae layers; conductance; infiltration

Conductance Enhancement of Nano-Particulate Indium Tin Oxide Layers Fabricated by Printing Technique - Groß, Michael; Maksimenko, Ilja; Faber, Hendrik; Linse, N.; Wellmann, Peter (Nanotech 2008, Vol. 1-3, 2008)
To understand the mechanisms behind the conductance improvement and to fathom the limits we did some investigations: long-term resistance measurements gave an insight in oxygen vacancy balance concentration. From infrared absorption measurements we inferred the free charge carrier density and at present we carry out XPS measurements which yield information about the alteration of oxygen vacancy concentration. Considering these data we discuss two conductance improving mechanisms: The increase of the free charge carrier density by a rise of oxygen vacancy concentration as well as a release of trapped charge carriers from the aggregate surface
Keywords: ITO; nanoparticles; transmittance; conductance

Conductivity and adhesion enhancement in low-temperature processed indium tin oxide/polymer nanocomposites - Maksimenko, Ilja; Groß, Michael; Königer, Tobias; Münstedt, Helmut; Wellmann, Peter (Thin Solid Films, 2010)
We report on the conductivity and adhesion enhancement of indium tin oxide (In(2)O(3):Sn; ITO) nanoparticle films by the application of polymers as matrix material. We fabricated ITO layers at a maximum process temperature of 130 degrees C by modifying and spin-coating nanoparticulate ITO dispersions. Dispersions containing the organic film-forming agent polyvinylpyrrolidone (PVP) and the organofunctional coupling agent 3-methacryloxypropyltrimethoxysilane (MPTS) have been developed to obtain transparent and conducting coatings on substrates which do not withstand high process temperatures like polymers or already processed glasses. The layers were cured by UV-irradiation as well as by low-temperature heat treatment (T = 130 degrees C) in air and under forming gas atmosphere (N(2)/H(2)). The influence of the additives on the electrical, optical, morphological and mechanical layer properties is reported. Compared to best pure ITO layers (3.1 Omega(-1)cm(-1)), the ITO-MPTS-PVP nanocomposite coatings exhibit a conductance of 9.8 Omega(-1)cm(-1). Stable sheet resistances of 750 Omega/square at a coexistent transmittance of 86% at 550 nm for a layer thickness of about 1.3 mu m were achieved. The conductance enhancement is a consequence of the consolidation of the ITO nanoparticle network due to the acting shrinkage forces caused either by drying in the case of PVP or UV-irradiation induced condensation and polymerization reactions in the case of MPTS. (C) 2009 Elsevier B.V. All rights reserved.
Keywords: Indium tin oxide (ITO); Nanoparticles; Polyvinylpyrrolidone (PVP); 3-Methacryloxypropyltrimethoxysilane (MPTS); Nanocomposite; Adhesion

Consensus statement for stability assessment and reporting for perovskite photovoltaics based on ISOS procedures - Khenkin, Mark V.; Katz, Eugene A.; Abate, Antonio; Bardizza, Giorgio; Berry, Joseph J.; Brabec, Christoph; Brunetti, Francesca; Bulovic, Vladimir; Burlingame, Quinn; Di Carlo, Aldo; Cheacharoen, Rongrong; Cheng, Yi-Bing; et al. (Nature Energy, 2020)
Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.
CRIS-Team Scopus Importer:2020-02-04

Consensus statement: Standardized reporting of power-producing luminescent solar concentrator performance - Yang, Chenchen; Atwater, Harry A.; Baldo, Marc A.; Baran, Derya; Barile, Christopher J.; Barr, Miles C.; Bates, Matthew; Bawendi, Moungi G.; Bergren, Matthew R.; Borhan, Babak; Brabec, Christoph; Brovelli, Sergio; et al. (Joule, 2022)
Fair and meaningful device performance comparison among luminescent solar concentrator-photovoltaic (LSC-PV) reports cannot be realized without a general consensus on reporting standards in LSC-PV research. Therefore, it is imperative to adopt standardized characterization protocols for these emerging types of PV devices that are consistent with other PV devices. This commentary highlights several common limitations in LSC literature and summarizes the best practices moving forward to harmonize with standard PV reporting, considering the greater nuances present with LSC-PV. Based on these practices, a checklist of actionable items is provided to help standardize the characterization/reporting protocols and offer a set of baseline expectations for authors, reviewers, and editors. The general consensus combined with the checklist will ultimately guide LSC-PV research towards reliable and meaningful advances.
CRIS-Team WoS Importer:2022-02-11

Contactless electrical defect characterization and topography of a-plane grown epitaxial layers - Wagner, M.; Mustafa, E.; Hahn, S.; Syväjärvi, Mikael; Yakimova, Rositsa; Jang, Yeon-Suk; Sakwe, Aloysius; Wellmann, Peter (Materials Science Forum, 2007)
Keywords: Contactless characterization; Sublimation epitaxy; Photo induced current transient spectroscopy; Photoluminescence

Contactless temperature determination using dual-channel lock-in phosphor thermometry - Hashemi, Amir; Jovicic, Gordana; Batentschuk, Miroslaw; Brabec, Christoph; Vetter, Andreas (Measurement Science and Technology, 2017)
In this paper, we present dual-channel lock-in phosphor thermometry, which offers an option of accurate and contactless temperature determination under high environmental noise. We studied YAG:Dy as thermographic phosphor at an excitation wavelength of 405 nm. We tested our approach under different experimental conditions with noise levels of about 550, 1060 and 2190 times larger than the excitation signal. With the dual-channel lock-in setup, we were able to suppress the strong noise in all cases and to reliably determine surface temperature using our optical measurements (error < 10 K). Additionally, the effect of signal to noise ratio, lock-in frequency and lock-in bandwidth on temperature determination accuracy was studied in this work.
Keywords: dual-channel; lock-in; luminescence; phosphor thermometry; temperature

Controlling additive behavior to reveal an alternative morphology formation mechanism in polymer: Fullerene bulk-heterojunctions - Güldal, Nusret Sena; Berlinghof, Marvin; Kassar, Thaer; Du, Xiaoyan; Jiao, Xuechen; Meyer, Markus; Ameri, Tayebeh; Osvet, Andres; Li, Ning; Destri, Giovanni Li; Fink, Rainer; Ade, Harald; et al. (Journal of Materials Chemistry A, 2016)
One of the most employed morphology optimization methods to design better performing organic photovoltaic devices is ink formulation engineering with additives. In this work, by employing a suboptimal host solvent mixture and 1,8-diiodooctane (DIO) as a very optimal solvent for both components in poly-thieno[3,2b]thiophene-diketopyrrolopyrrole-co-thiophene (DPP-TT-T)-based bulk-heterojunctions (BHJ), an alternative, previously unknown mechanism of additive behavior on BHJ microstructure formation is presented. In situ characterization methods involving grazing incidence X-ray diffraction, white-light reflectometry, laser light scattering and photoluminescence during film drying reveal that the microstructure formation under the influence of DIO is led towards thermodynamic equilibrium during host solvent drying, and the kinetics of morphology formation (i.e. polymer crystallization, fullerene aggregation...) are controlled dominantly by the additive during its evaporation. Ex situ X-ray-based characterization methods, such as scanning transmission X-ray microspectroscopy (STXM) and resonant soft X-ray scattering (R-SoXS), additionally reveal that the microstructure of dried films favors smaller domain sizes with purer domains, smaller fullerene aggregates, bimodal polymer crystallization relative to the substrate and more face-on molecular orientation relative to the donor/acceptor interface, which at the end lead to better performing devices with power conversion efficiencies ranging from 1.25% to 4.68%.
Keywords: Engineering controlled terms: Additives; Fullerenes; Heterojunctions; Interfaces (materials); Light scattering; Microstructure; Molecular orientation; Morphology; Polymers; Solvents; Thiophene; X ray diffraction; X ray scattering Bulk heterojunction (BHJ); Characterization methods; Donor/acceptor interface; Grazing incidence X-ray diffraction; In-situ characterization; Microstructure formation; Organic photovoltaic devices; Power conversion efficiencies Engineering main heading: Polymer films

Controlling Intermediate Phase Formation to Enhance Photovoltaic Performance of Inverted FA-Based Perovskite Solar Cells - Li, Chaohui; Park, Hyoungwon; Qiu, Shudi; Streller, Fabian; Zhang, Kaicheng; Peng, Zijian; Byun, Jiwon; Tian, Jingjing; Maiti, Santanu; Xie, Zhiqiang; Dong, Lirong; Liu, Chao; et al. (ACS Energy Letters, 2024)
Formamidinium (FA)-based perovskites exhibit significant potential for highly efficient photovoltaics due to their promising optoelectronic properties and optimal bandgap. However, the undesired inactive phase arises from multiple crystal nucleation pathways formed by various intermediate phases during the film formation process, persistently accompanying it. FA-based perovskites frequently struggle to form uniform, highly crystalline films. This challenge complicates the development of reliable and highly reproducible crystallization processes for perovskites and the establishment of guidelines for controlling the α-phase formation. In this work, we investigate the role of poly(acrylonitril-co-methyl acrylate) (PAM) to simultaneously control nucleation and subsequent α-phase crystallization. This successfully demonstrates the regulation of oriented crystal growth through the creation of a PAM-PbI2 intermediate. Ultimately, PAM-modified p-i-n architecture devices obtain a promising power conversion efficiency (PCE) of 25.30%, with VOC (1.211 V), achieving 95% of the detailed balance limit. Additionally, PAM-modified devices maintain ≥90% of the initial efficiency for 1000 h under 1 sun and 65 °C operation.
CRIS-Team Scopus Importer:2024-11-22

Controlling the crystallization dynamics of photovoltaic perovskite layers on larger-area coatings - Zeng, Linxiang; Chen, Shi; Forberich, Karen; Brabec, Christoph; Mai, Yaohua; Guo, Fei (Energy and Environmental Science, 2020)
As perovskite solar cells are highly efficient and already meet the efficiency requirement for renewable power generation, more attention is given to technological barriers such as scalability and stability. In particular, the large efficiency losses associated with upscaling lab-scale devices to large-area modules represents one of the major hurdles for commercialization. Given the essential role of the perovskite films in the device performance, it is of critical importance to develop reliable crystallization protocols to deposit high-quality perovskite layers via scalable methods. This review summarizes recent advances in emerging crystallization protocols for the large-scale deposition of perovskite thin films. The unique merits of the well-developed crystallization strategies, including antisolvent, gas quenching, vacuum quenching, etc., are carefully analyzed and discussed. We highlight that, independent of the coating method, creating intermediate phases to decouple the otherwise overlapped solution coating and crystal growth is essential to realize homogeneous coatings of perovskite thin films. Strategies for enhancing the crystal morphology of perovskite films are presented as well, which is vitally important to realize reproducible manufacturing of large-area modules. This tutorial review assists the screening and development of robust crystallization strategies for scalable deposition of high-quality perovskite films for photovoltaic applications.<br

Controlling the electronic interface properties in polymer–fullerene bulk heterojunction solar cells - Wolf, Nadine; Manara, Jochen; Stubhan, Tobias; Dyakonov, Vladimir; Brabec, Christoph (Springer New York LLC, 2016)
This work covers the use of solution-processed metal oxides as interface layers for organic solar cells. To study the interface properties, intrinsic and Al-doped ZnO were chosen as reference systems. From the class of n-type metal oxides, ZnO was chosen because it can be doped when it is solution processed. Furthermore, the influence of thin modification layers applied on top of the metal oxides is investigate
Keywords: Aluminum-doped zinc oxide; Barium hydroxide; Charge transport in nanoparticular films; Conjugated polyelectrolyte; Device structure; Diketopyrrolopyrrole-quinquethiophene; Doped zinc oxide; Electronic surface properties; Energy diagram; Energy-level diagrams; EQE spectra; Inferface layers for organic solar cells; Interface layers; Interface modification layers; Inverted organic solar cells; J-V characteristics; Low temperature; Molybdenum oxide; Mott–Schottky capacitance; Oxygen; P3HT; PCDTBT; Phosphonic acid anchored fullerene SAM; Polyvinylpyrrolidone; Poole–Frenkel effect; Reference solar cells; SAM modification; Stability of interface materials; Stabilization of AZO nanoparticles; Summary; Thickness dependence; Trioxadecanoic acid; Water; Zinc oxide

Correction: A star-shaped D-π-A small molecule based on a tris(2-methoxyphenyl)amine core for highly efficient solution-processed organic solar cells - Min, Jie; Luponosov, Yuriy N.; Solodukhin, Alexander N.; Kausch-Busies, Nina; Ponomarenko, Sergei A.; Ameri, Tayebeh; Brabec, Christoph (Journal of Materials Chemistry C, 2014)
Correction for 'A star-shaped D-π-A small molecule based on a tris(2-methoxyphenyl)amine core for highly efficient solution-processed organic solar cells' by Jie Min et al., J. Mater. Chem. C, 2014, 2, 7614-7620. This journal is

Correction: Balancing electrical and optical losses for efficient 4-terminal Si-perovskite solar cells with solution processed percolation electrodes (Journal of Materials Chemistry A (2018) 6 (3583-3592) DOI: 10.1039/C7TA10945H) - Ramírez Quiroz, César Omar; Shen, Yilei; Salvador, Michael Filipe; Forberich, Karen; Schrenker, Nadine; Spyropoulos, Georgios; Heumüller, Thomas; Wilkinson, Benjamin; Kirchartz, Thomas; Spiecker, Erdmann; Verlinden, Pierre J.; Zhang, Xueling; et al. (Journal of Materials Chemistry A, 2018)
The authors regret inconsistent labelling of the Jsc column in Table 1 of the original manuscript. The experimental conditions are now described correctly in the caption of the updated Table 1, shown below, as indicated by superscripts "b" and "c". (Table Presented). The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers

Correction to: Polymer-acid-metal quasi-ohmic contact for stable perovskite solar cells beyond a 20,000-hour extrapolated lifetime (Nature Communications, (2024), 15, 1, (2002), 10.1038/s41467-024-46145-7) - Luo, Junsheng; Liu, Bowen; Yin, Haomiao; Zhou, Xin; Wu, Mingjian; Shi, Hongyang; Zhang, Jiyun; Elia, Jack; Zhang, Kaicheng; Wu, Jianchang; Xie, Zhiqiang; Liu, Chao; et al. (Nature Communications, 2024)
Correction to: Nature Communicationshttps://doi.org/10.1038/s41467-024-46145-7, published online 05 March 2024 In this article, Junsheng Luo and Bowen Liu should have been denoted as equally contributing authors. The original article has been corrected.
CRIS-Team Scopus Importer:2024-05-17

Correlation between the generated string powers of a photovoltaic: Power plant and module defects detected by aerial thermography - Dalsass, Manuel; Scheuerpflug, Hans; Fecher, Frank W.; Buerhop-Lutz, Claudia; Camus, Christian; Brabec, Christoph (43rd IEEE Photovoltaic Specialists Conference, PVSC 2016, 2016)
Drone-based aerial thermography has become a convenient quality assessment tool for photovoltaic power plants. Often caused by defective photovoltaic modules and cells, thermal abnormalities can be localized and classified. So far, infrared images cannot be utilized for the quantitative estimation of the generated power of a solar park yet. In this context, three photovoltaic power plants with an overall nominal power of approximately 9.4 MW are evaluated. The analysis of both the radiometric data and the monitoring data of the inverters indicate a strong correlation between defective modules and the power of the associated string.
Keywords: aerial thermography; monitoring; PV module defects; system performance

Correlation between the generated string powers of a photovoltaic power plant and module defects detected by aerial thermography - Dalsass, Manuel; Scheuerpflug, Hans; Fecher, Frank W.; Buerhop-Lutz, Claudia; Camus, Christian; Brabec, Christoph (44th IEEE Photovoltaic Specialist Conference, PVSC 2017, 2018)
Drone-based aerial thermography has become a convenient quality assessment tool for photovoltaic power plants. Often caused by defective photovoltaic modules and cells, thermal abnormalities can be localized and classified. So far, infrared images cannot be utilized for the quantitative estimation of the generated power of a solar park yet. In this context, three photovoltaic power plants with an overall nominal power of approximately 9.4 MWp are evaluated. The analysis of both the radiometric data and the monitoring data of the inverters indicate a strong correlation between defective modules and the power of the associated stri
Keywords: Aerial thermography; PV module defects; Monitoring; System performance

Correlative relationship between nanomorphology, crystallinity, texture and device efficiency of organic BHJ solar cells studied by energy-filtered TEM - Harreiß, Christina; Wu, Mingjian; Langner, Stefan; Rechberger, Stefanie; Will, Johannes; Brabec, Christoph; Spiecker, Erdmann (Microscopy and Microanalysis, 2021)

Cost analysis of roll-to-roll fabricated ITO free single and tandem organic solar modules based on data from manufacture - Machui, Florian; Hosel, Markus; Li, Ning; Spyropoulos, Georgios; Ameri, Tayebeh; Sondergaard, Roar R.; Jorgensen, Mikkel; Scheel, Arnulf; Gaiser, Detlef; Kreul, Kilian; Lenssen, Daniel; Legros, Mathilde; et al. (Energy and Environmental Science, 2014)
We present a cost analysis based on state of the art printing and coating processes to fully encapsulated, flexible ITO- and vacuum-free polymer solar cell modules. Manufacturing data for both single junctions and tandem junctions are presented and analyzed. Within this calculation the most expensive layers and processing steps are identified. Based on large roll-to-roll coating experiments the exact material consumptions were determined. In addition to the data for the pilot scale experiment presented here, projections to medium and large scale scenarios serve as a guide to achieve cost targets of 5 €ct per W in a detailed material and cost analysis. These scenarios include the replacement of cost intensive layers, as well as process optimization steps. Furthermore, the cost structures for single and tandem devices are listed in detail and discussed. In an optimized model the material costs drop below 10 € per m which proves that OPV is a competitive alternative to established power generation technologies. This journal is © the Partner Organisations 2014.
Keywords: Engineering controlled terms: Coatings; Costs; Experiments; Manufacture; Optimization; Rolls (machine components); Solar cells Coating process; Optimized models; Pilot-scale experiments; Polymer Solar Cells; Power generation technology; Processing steps; Single junction; Tandem junction Engineering main heading: Cost accounting GEOBASE Subject Index: coating; cost-benefit analysis; numerical model; photovoltaic system; solar power

Cost-efficient recycling of organic photovoltaic devices - Sun, Rui; Yuan, Xinxin; Yang, Xinrong; Wu, Yao; Shao, Yiming; Wu, Xiaohei; Brabec, Christoph; Min, Jie (Joule, 2024)
The vast majority of research on organic photovoltaics (OPVs) has focused on improving device efficiency and stability and reducing material costs. However, if one could refurbish OPVs, their stability might not be so demanding, and the reuse of valuable OPV components can reduce the price per watt of solar modules. Herein, we present a dismantling procedure for reusing the active-layer materials without causing performance losses and for recovering the silver electrode and indium tin oxide (ITO)-electrode substrate via chemical and physical processes. Combined with the developed physical mixing methodology, the OPVs fabricated from recycled components also show comparable performance to that of fresh devices. The potential economic analysis points out that this recycling protocol can save 14.24 m−2 in industrial scenarios, strongly demonstrating the possibility of recycling OPVs. This work represents a significant step toward cost-effective, high-yield recycling of waste OPVs while also demonstrating the prospects of no material supply constraints for OPV manufacturing shortly.
CRIS-Team Scopus Importer:2024-07-19
Keywords: economic feasibility; organic photovoltaics; recycling protocol; reuse of materials; sustainability

Cradle to Cradle Recycling of Perovskite Solar Cells - Wu, Zhenni; Babayeva, Gülüsüm; Zhang, Jiyun; Sytnyk, Mykhailo; Hauch, Jens; Brabec, Christoph; Peters, Ian Marius (Conference Record of the IEEE Photovoltaic Specialists Conference, 2023)
Cradle-to-cradle recycling plays an important role in resolving one of the major upcoming challenges for photovoltaics in the energy transition-resource management. As photovoltaic production continues to grow, it absorbs a vast amount of resources. Cradle-to-cradle recycling is essential to keep these resources available perpetually and minimize waste generation. To achieve this, a new design paradigm for solar panels that puts recycling in its center is needed. In this study, we show first results of a perovskite solar cell that was created using such a design paradigm. We created a device with 18.1% efficiency and an architecture that facilitates disassembly of the functional layers. We show that the absorber material, MaPbI3 was used for the test device, can be recycled without causing a loss of solar cell efficiency.
CRIS-Team Scopus Importer:2024-12-16

Creation and identification of the two spin states of dicarbon antisite defects in 4H-SiC - Steeds, J. W.; Sullivan, W.; Furkert, S. A.; Evans, G. A.; Wellmann, Peter (Physical Review B, 2008)
This paper deals with the positive identification by low-temperature photoluminescence microspectroscopy of the two spin states of the dicarbon antisites in 4H-SiC. The defects are created by high-dose electron irradiation at room temperature or by subsequent exposure to intense 325 nm radiation at temperatures up to 1300 degrees C. Identification was achieved by their formation and annealing characteristics, by the energies of their local vibrational modes, by the nature of their splitting in (13)C isotope enriched samples, and by comparison with published results of ab initio local density approximation calculations. Four related but different forms of this defect have been predicted, two with S = 0 and two with S = 1, and their calculated properties are consistent with the experimental results presented here. The excitation processes for the optical centers within the irradiated region are quite unusual. For a 488 nm laser excitation, both spin states of the defect are observed by up-conversion. For a 325 nm excitation, the optical centers are only observed at the periphery of the high-dose irradiatedregions after the sample has been exposed to an intense 325 nm beam. In this case, the optical centers are mainly in the S=0 state. The centers are eliminated by annealing in the range of 800-950 degrees C.
Keywords: Silicon carbide; 4H SiC; defects; dicarbon antisite defect; photoluminescence; spin states

Creation of storage centers in CsBr: Eu2+ needle image plates by vacuum ultraviolet radiation - Weidner, Martina; Batentschuk, Miroslaw; Osvet, Andres; Winnacker, Albrecht; Tahon, J. P.; Leblans, P. (Journal of Applied Physics, 2009)
In this study, the photostimulated luminescence of the CsBr:Eu2+ needle image plates (NIPS) after vacuum ultraviolet (VUV) irradiation and their photoluminescence under VUV and UV excitation were investigated. It was shown that the photostimulable storage centers arise almost exclusively due to irradiation of the CsBr:Eu NIPs in the spectral lines of creation of the 4p55s anion excitons, and not in the region of interband transitions of CsBr. The explanation of the results is based mainly on the radiative and nonradiative decay of the self-localized e+Br_2- excitons.

Critical review of the molecular design progress in non-fullerene electron acceptors towards commercially viable organic solar cells. - Wadsworth, Andrew; Moser, Maximilian; Marks, Adam; Little, Mark S.; Gasparini, Nicola; Brabec, Christoph; Baran, Derya; Mcculloch, Iain (Chemical Society Reviews, 2018)
Fullerenes have formed an integral part of high performance organic solar cells over the last 20 years, however their inherent limitations in terms of synthetic flexibility, cost and stability have acted as a motivation to develop replacements; the so-called non-fullerene electron acceptors. A rapid evolution of such materials has taken place over the last few years, yielding a number of promising candidates that can exceed the device performance of fullerenes and provide opportunities to improve upon the stability and processability of organic solar cells. In this review we explore the structure-property relationships of a library of non-fullerene acceptors, highlighting the important chemical modifications that have led to progress in the field and provide an outlook for future innovations in electron acceptors for use in organic photovoltaics.

Crystal Damage and Surface Morphology in Industrial Diamond Wire Slicing of 300 mm Monocrystalline Silicon Wafers for Microelectronic Devices - Oberhans, Stephan; Heiß, Wolfgang; Pietsch, Georg J. (Advanced Materials Technologies, 2024)
In the semiconductor industry, thin wafers are cut from a monocrystalline silicon. The most important process step is cutting the monocrystal into a multitude of thin substrate slices, which determines the properties of the resulting wafers. Some time ago, the transition from traditional slurry-wire-slicing (S-MWS) to diamond-wire-slicing (D-MWS), which is more cost-effective and resource-efficient, took place. Unlike in the photovoltaic industry and also in the production of smaller wafer diameters of up to 200 mm, it is not possible to create a seamless transition with today's standard wafer diameters of 300 mm due to the waviness that occurs on the wafer surface immediately after the cutting process. This situation considerably limits the achievable component generation (design rule), as the strict requirements of the chip manufacturers cannot be fulfilled. Therefore, a comprehensive understanding of the process is required. A detailed comparison of the surface structure, surface topography, and fracture strength is carried out based on the three relevant crystal orientations Silicon(100), Silicon(110), and Silicon(111). In addition, some wire segments are examined. All microscopic examinations carry out on both the primary and secondary chipping faces do not provide any correlation between the microscopic surface condition and the macroscopic waviness.
CRIS-Team Scopus Importer:2025-02-04
Keywords: diamond-wire-slicing (D-MWS); material removal mechanism; multi-wire-slicing (MWS); primary and secondary chipping face; silicon

Crystallization and investigation of the structural and optical properties of ce3+-doped y3−xcaxal5−ysiyo12 single crystalline film phosphors - Gorbenko, Vitalii; Zorenko, Tetiana; Witkiewicz-Łukaszek, Sandra; Shakhno, Anna; Osvet, Andres; Batentschuk, Miroslaw; Fedorov, Aleksandr; Zorenko, Yuriy (Crystals, 2021)
This work is devoted to the crystallization and investigation of the optical properties of single crystalline films (SCFs) of Ce3+-doped Y3−xCaxAl5−ySiyO12 garnet, where the content of Ca2+ and Si4+ cations varied in the x = 0.13–0.52 and y = 0.065–0.5 ranges, respectively. The SCF samples were grown using the liquid phase epitaxy technique onto Y3Al5O12 substrates from the melt solution with equimolar Ca and Si content using PbO-B2O3 flux. However, the Ca and Si concentration in Y3−xCax Al5−ySiyO12: Ce SCFs is not equal: The Ca2+ content was systematically larger than that of Si4+, and the Ca2+ excess is compensated for by the Ce4+ ion formation. The absorption, scintillation, and luminescent properties of Y3−xCaxAl5−ySiyO12: Ce SCFs with different Ca/Si concentrations were investigated and compared with the sample of YAG: Ce SCF. Due to the creation of Ce4+ ions, the as-grown Y3−xCaxAl5−ySiyO12: Ce SCFs show relatively low light yield (LY) under α–particle excitation but a fast scintillation response with a decay time in the ns range. After SCF annealing in the reducing (N2 + H2) atmosphere at T > 1000 °C, the recharging of Ce4+→Ce3+ ions occurs. Furthermore, the samples annealed at 1300 °C SCF possess an LY of about 40% in comparison with the reference YAG: Ce SCF and scintillation decay kinetics much closer to that of the SCF counterpart. Due to Ca2+ and Si4+ alloying, the Ce3+ emission spectra in Y3−xCaxAl5−ySiyO12 SCFs are extended to the red range in comparison with the spectra of YAG: Ce SCF. Such an extension is caused by the Ce3+ multicenter formation at the substitutions of both Y3+ and Ca2+ dodecahedral positions in the hosts of these mixed garnets.
CRIS-Team Scopus Importer:2021-07-30
Keywords: Ca; Ce; Liquid phase epitaxy; Single crystalline films; YAG garnet

Crystallization of sensitizers controls morphology and performance in Si-/C-PCPDTBT-sensitized P3HT: ICBA ternary blends - Du, Xiaoyan; Jiao, Xuechen; Rechberger, Stefanie; Perea Ospina, Jose Dario; Meyer, Markus; Kazerouni, Negar; Spiecker, Erdmann; Ade, Harald; Brabec, Christoph; Fink, Rainer; Ameri, Tayebeh (Macromolecules, 2017)
Organic solar cells based on multinary components are promising to further boost the device performance. The complex interplay of the morphology and functionality needs further investigations. Here, we report on a systematic study on the morphology evolution of prototype ternary systems upon adding sensitizers featuring similar chemical structures but dramatically different crystallinity, namely poly(3-hexylthiophene) (P3HT) and indene-C-bis-adduct (ICBA) blends with poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadi-azole)-5,5′-diyl] (Si-PCPDTBT) and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (C-PCPDTBT), employing energy-filtered transmission electron microscopy (EFTEM) and resonant soft X-ray scattering (RSoXS). In addition, a combined density functional theory (DFT) and artificial neuronal network (ANN) computational approach has been utilized to calculate the solubility parameters and Flory-Huggins intermolecular parameters to evaluate the influence of miscibility on the final morphology. Our experiments reveal that the domain spacing and purity of ICBA-rich domains are retained in Si-PCPDTBT-based systems but are strongly reduced in C-PCPDTBT-based ternary systems. The P3HT fiber structure are retained at low sensitizer content but dramatically reduced at high sensitizer content. The theoretical calculations reveal very similar miscibility/compatibility between the two sensitizers and ICBA as well as P3HT. Thus, we conclude that mainly the crystallization of Si-PCPDTBT drives the nanostructure evolution in the ternary systems, while this driving force is absent in C-PCPDTBT-based ternary blends.
Keywords: Computation theoryDeep neural networksHigh resolution transmission electron microscopyMorphologyNeuronsOrganic solar cellsSiliconSolar cellsSolubilityTernary systemsTransmission electron microscopyX ray scattering

Crystal Phase Transitions in the Shell of PbS/CdS Core/Shell Nanocrystals Influences Photoluminescence Intensity - Lechner, Rainer T.; Fritz-Popovski, Gerhard; Yarema, Maksym; Heiß, Wolfgang; Hoell, Armin; Schuelli, Tobias U.; Primetzhofer, Daniel; Eibelhuber, Martin; Paris, Oskar (Chemistry of Materials, 2014)
We reveal the existence of two different crystalline phases, i.e., the metastable rock salt and the equilibrium zinc blende phase within the CdS-shell of PbS/CdS core/shell nanocrystals formed by cationic exchange. The chemical composition profile of the core/shell nanocrystals with different dimensions is determined by means of anomalous small-angle X-ray scattering with subnanometer resolution and is compared to X-ray diffraction analysis. We demonstrate that the photoluminescence emission of PbS nanocrystals can be drastically enhanced by the formation of a CdS shell. Especially, the ratio of the two crystalline phases in the shell significantly influences the photoluminescence enhancement. The highest emission was achieved for chemically pure CdS shells below 1 nm thickness with a dominant metastable rock salt phase fraction matching the crystal structure of the PbS core. The metastable phase fraction decreases with increasing shell thickness and increasing exchange times. The photoluminescence intensity depicts a constant decrease with decreasing metastable rock salt phase fraction but shows an abrupt drop for shells above 1.3 nm thickness. We relate this effect to two different transition mechanisms for changing from the metastable rock salt phase to the equilibrium zinc blende phase depending on the shell thickness. © 2014 American Chemical Societ
Keywords: Core/shell nanocrystals; Crystal phase transition; Photoluminescence intensities

Crystal-structure of active layers of small molecule organic photovoltaics before and after solvent vapor annealing - Berlinghof, Marvin; Langner, Stefan; Harreiß, Christina; Schmidt, Ella; Siris, Rita; Bertram, Florian; Shen, Chen; Will, Johannes; Schindler, Torben; Prihoda, Annemarie; Rechberger, Stefanie; Duesberg, Georg; et al. (Zeitschrift fur Kristallographie - Crystalline Materials, 2020)
It is demonstrated by a detailed structural analysis that the crystallinity and the efficiency of small molecule based organic photovoltaics can be tuned by solvent vapor annealing (SVA). Blends made of the small molecule donor 2,2′-[(3,3′″,3″″,4′-tetraoctyl[2,2′:5′,2″:5″,2′″:5′″,2″″-quinquethiophene]-5,5″″-diyl)bis[(Z)-methylidyne(3-ethyl-4-oxo-5,2-thiazolidinediylidene)]]bis-propanedinitrile (DRCN5T) and the acceptor [6,6]-phenyl C71 butyric acid methyl ester (PC 71 BM) were annealed using solvent vapors with either a high solubility for the donor (tetrahydrofuran), the acceptor (carbon disulfide) or both (chloroform). The samples were analyzed by grazing-incidence wide-angle X-ray scattering (GIWAXS), electron diffraction, X-ray pole figures, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). A phase separation of DRCN5T and PC 71 BM is induced by SVA leading to a crystallization of DRCN5T and the formation of a DRCN5T enriched layer. The DRCN5T crystallites possess the two dimensional oblique crystal system with the lattice parameters a = 19.2 Å, c = 27.1 Å, and β = 111.1° for the chloroform case. No major differences in the crystal structure for the other solvent vapors were observed. However, the solvent choice strongly influences the size of the DRCN5T enriched layer. Missing periodicity in the [010]-direction leads to the extinction of all Bragg reflections with k ≠ 0. The annealed samples are randomly orientated with respect to the normal of the substrate (fiber texture

Cs2AgxNa1-xBiyIn1-yCl6 perovskites approaching photoluminescence quantum yields of 100% - Stroyuk, Oleksandr; Raievska, Oleksandra; Barabash, Anastasia; Kupfer, Christian; Osvet, Andres; Dzhagan, Volodymyr; Zahn, Dietrich R. T.; Hauch, Jens; Brabec, Christoph J. (Materials Advances, 2022)
A new single-step and green approach for the synthesis of microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 (CANBIC) perovskites in ambient conditions is introduced. The CANBIC powders emit broadband self-trapped excitonic photoluminescence (PL) with a champion PL quantum yield (QY) of 98 +/- 2% and a PL lifetime of ca. 2 mu s observed for x = 0.40 and y = 0.01-0.02. The study focuses on the dependence of structural, spectral, and photophysical properties of CANBICs on Bi content. CANBICs are solid solutions with isomorphous In-to-Bi substitution with the bandgap and valence band edge energy decreasing gradually with increasing y. The PL QY and the rate constant of the radiative recombination showed volcano-shaped dependences on the Bi content, while the rate of the non-radiative recombination revealed a drastic growth by three orders of magnitude as the Bi fraction y was elevated from 0.01 to 1.0 indicating that BiCl6 units are responsible for non-radiative recombination.
CRIS-Team WoS Importer:2022-09-09

Cu2ZnSn(S,Se)(4) solar cells processed by rapid thermal processing of stacked elemental layer precursors - Lechner, R.; Jost, S.; Palm, J.; Gowtham, M.; Sorin, F.; Louis, B.; Yoo, Hye Sun; Wibowo, Rachmat Adhi; Hock, Rainer (ELSEVIER SCIENCE SA, 2013)
In this contribution we report on the development of a two-step process for the formation of Cu2ZnSn(S, Se)(4) thin films for solar cells. The two-step formation process of the pentanary kesterite consists of (i) sputter deposition of the metals Cu, Zn and Sn followed by thermal evaporation of chalcogen and (ii) rapid thermal processing of the metal/ chalcogen precursors in chalcogen containing ambient. After the absorber formation process, solar cells were processed by deposition of CdS buffer, window layer and metal grid. We evaluated different metal precursor compositions in the ternary Cu-Zn-Sn metal systems regarding their behavior as appropriate precursors for the crystallization of Cu2ZnSn(S, Se)(4) absorbers. X-ray diffraction analyses show the presence of secondary chalcogenide phases in absorbers with Cu-poor composition. In combination with Raman spectroscopy, the efficient sulfoselenization could be demonstrated. A broad compositional region is found giving cell efficiencies above 6% via this process route and the potentials for further improvements are discussed. The best solar cell measured so far reached 6.6% efficiency on 1.34 cm(2) cell size. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: Cu2ZnSn(S; Se)(4); Kesterite; Sulfo-selenization; Solar cells

Cubic silicon carbide as a potential photovoltaic material - Syväjärvi, Mikael; Ma, Quanbao; Jokubavicius, Valdas; Galeckas, Augustinas; Sun, Jianwu; Liu, Xinyu; Jansson, Mattias; Wellmann, Peter; Linarsson, Margareta; Runde, Paal; Johansen, Bertil Andre; Thøgersen, Annett; et al. (Solar Energy Materials and Solar Cells, 2016)
In this work we present a significant advancement in cubic silicon carbide (3C-SiC) growth in terms of crystal quality and domain size, and indicate its potential use in photovoltaics. To date, the use of 3C-SiC for photovoltaics has not been considered due to the band gap of 2.3 eV being too large for conventional solar cells. Doping of 3C-SiC with boron introduces an energy level of 0.7 eV above the valence band. Such energy level may form an intermediate band (IB) in the band gap. This IB concept has been presented in the literature to act as an energy ladder that allows absorption of sub-bandgap photons to generate extra electron–hole pairs and increase the efficiency of a solar cell. The main challenge with this concept is to find a materials system that could realize such efficient photovoltaic behavior. The 3C-SiC bandgap and boron energy level fits nicely into the concept, but has not been explored for an IB behavior. For a long time crystalline 3C-SiC has been challenging to grow due to its metastable nature. The material mainly consists of a large number of small domains if the 3C polytype is maintained. In our work a crystal growth process was realized by a new approach that is a combination of initial nucleation and step-flow growth. In the process, the domains that form initially extend laterally to make larger 3C-SiC domains, thus leading to a pronounced improvement in crystalline quality of 3C-SiC. In order to explore the feasibility of IB in 3C-SiC using boron, we have explored two routes of introducing boron impurities; ion implantation on un-doped samples and epitaxial growth on un-doped samples using pre-doped source material. The results show that 3C-SiC doped with boron is an optically active material, and thus is interesting to be further studied for IB behavior. For the ion implanted samples the crystal quality was maintained even after high implantation doses and subsequent annealing. The same was true for the samples grown with pre-doped source material, even with a high concentration of boron impurities. We present optical emission and absorption properties of as-grown and boron implanted 3C-SiC. The low-temperature photoluminescence spectra indicate the formation of optically active deep boron centers, which may be utilized for achieving an IB behavior at sufficiently high dopant concentrations. We also discuss the potential of boron doped 3C-SiC base material in a broader range of applications, such as in photovoltaics, biomarkers and hydrogen generation by splitting water.
Keywords: Intermediate band; Silicon carbide; Solar cell; Photovoltaic; Boron Doping; 3C-SiC; Cubic

Cutting “lab-to-fab” short: high throughput optimization and process assessment in roll-to-roll slot die coating of printed photovoltaics - Wagner, Michael; Distler, Andreas; Le Corre, Vincent Marc; Zapf, Simon; Baydar, Burak; Schmidt, Hans-Dieter; Heyder, Madeleine; Forberich, Karen; Lüer, Larry; Brabec, Christoph; Egelhaaf, Hans-Joachim (Energy and Environmental Science, 2023)
Commercialization of printed photovoltaics requires knowledge of the optimal composition and microstructure of the single layers, and the ability to control these properties over large areas under industrial conditions. While microstructure optimization can be readily achieved by lab scale methods, the transfer from laboratory scale to a pilot production line (“lab to fab”) is a slow and cumbersome process: first, the difficulty of operating structure-sensitive methods in-line impedes proper microstructure characterization, and second, the processing-functionality relationship must be redetermined for every material combination as the results obtained by typical lab-scale spin-coating cannot be directly transferred to other coating methods. Here, we show how we can optimize the performance of organic solar cells and at the same time assess process performance in a 2D combinatorial approach directly on an industrially relevant slot die coating line. This is enabled by a multi-nozzle slot die coating head allowing parameter variations along and across the web. This modification allows us to generate and analyze 3750 devices in a single coating run, varying the active layer donor : acceptor ratio and the thickness of the electron transport layer (ETL). We use Gaussian Process Regression (GPR) to exploit the whole dataset for precise determination of the optimal parameter combination. Performance-relevant features of the active layer morphology are inferred from UV-Vis absorption spectra. By mapping morphology in this way, small undesired gradients of process conditions (extrusion rates, annealing temperatures) are detected and their effect on device performance is quantified. The correlation between process parameters, morphology and performance obtained by GPR provides hints to the underlying physics, which are finally quantified by automated high-throughput drift-diffusion simulations. This leads to the conclusion that voltage losses which are observed for very thin ETL coatings are due to incomplete coverage of the electrode by the ETL, which causes enhanced surface recombination.
CRIS-Team Scopus Importer:2023-11-10

Damp-Heat–Induced Degradation of Lightweight Silicon Heterojunction Solar Modules With Different Transparent Conductive Oxide Layers - Zhang, Kai; Mashkov, Oleksandr; Yaqin, Muhammad Ainul; Doll, Bernd; Lambertz, Andreas; Bittkau, Karsten; Duan, Weiyuan; Peters, Ian Marius; Brabec, Christoph J; Rau, Uwe; Ding, Kaining (Progress in Photovoltaics, 2025)
Lightweight photovoltaic applications are essential for diversifying the solar energy supply. This opens up vast new scenarios for solar modules and significantly boosts the capacity of renewable energy. To ensure high efficiency and stability of the solar modules, several challenges need to be overcome. Degradation due to elevated temperature and/or humidity is a critical concern for silicon heterojunction (SHJ) solar modules. Here, we investigated the stability and degradation mechanism of encapsulated cells with lightweight configurations where the cells are based on three different types of transparent-conductive oxide (TCO): indium tin oxide (ITO), aluminum-doped zinc oxide (AZO), and a combination of ITO/AZO/ITO under humid and thermal environmental conditions. A damp heat (DH) test at a temperature of 85°C and relative humidity (RH) of 85% was performed on lightweight modules for 1000 h. Our results show that AZO is the most susceptible to DH degradation. The AZO film was damaged by the combined effects of moisture ingress and delamination of the interconnection foil, resulting in a decrease in the conductivity of the AZO film, leading to a dramatic increase in Rs and a decrease in FF of the modules. Consequently, moisture has a greater chance of percolating through the damaged AZO layer into the a-Si:H passivation layer, causing passivation degradation, which leads to an increase in recombination, resulting in a decrease in Voc of the modules. In particular, after capping the AZO film with an ITO film, the efficiency loss of the ITO/AZO/ITO module was significantly reduced. This suggests that the ITO film could be a promising protective capping layer for the AZO-based solar cells.
CRIS-Team Scopus Importer:2025-01-31
Keywords: AZO; damp-heat–induced degradation (DHID); lightweight module; reliability; silicon heterojunction

Data-Filtering-Dependent Variability of Long-Term Degradation Rates of MW-Scale Photovoltaic Power Plants from “Non-Ideal” Monitoring and Weather Data - Camus, Christian; Huettner, Maximilian; Lassahn, D.; Kurz, C.; Hauch, Jens; Brabec, Christoph (35th European Photovoltaic Solar Energy Conference and Exhibition, 2018)
In contrast to research photovoltaic (PV) systems, commercial PV systems are usually not equipped with sophisticated weather metrology and quite frequently even lack an irradiance sensor. Still, the determination of their degradation rate is of paramount importance for the plant owners. This paper compares various approaches to determine the degradation rates of commercial MW-scale PV systems from such “non-ideal” data sets as they are frequently obtained from monitoring data. In particular, the use of model-based irradiance and temperature data is evaluated and several novel methods for data filtering are introduced. It is investigated, for which weather conditions the use of externally weather station data is superior to on-site data. By reducing the data set to mostly sunny conditions, reliable DRs can be determined. Furthermore, the data scattering can be reduced significantly so that sudden performance drops or changes in the DRs become visible, which were previously masked by scattering and data drifts. These results demonstrate that significantly different DRs and uncertainties are obtained depending on the method of data filtering. Hence, care must be taken, when deriving DRs from “non-ideal” monitoring and weather data and when comparing DRs determined by different metho
Keywords: PV Technologies; Outdoor Performance; Yield Analysis; Temperature Behavior

Deciphering the Origins of P1-Induced Power Losses in CIGS Modules Through Hyperspectral Luminescence - Quiroz, César Omar Ramírez; Dion-Bertrand, Laura Isabelle; Brabec, Christoph; Müller, Joachim; Orgassa, Kay (Engineering, 2020)
In this report, we show that hyperspectral high-resolution photoluminescence mapping is a powerful tool for the selection and optimization of the laser ablation processes used for the patterning interconnections of subcells on Cu(Inx,Ga1−x)Se2 (CIGS) modules. In this way, we show that in-depth monitoring of material degradation in the vicinity of the ablation region and the identification of the underlying mechanisms can be accomplished. Specifically, by analyzing the standard P1 patterning line ablated before the CIGS deposition, we reveal an anomalous emission-quenching effect that follows the edge of the molybdenum groove underneath. We further rationalize the origins of this effect by comparing the topography of the P1 edge through a scanning electron microscope (SEM) cross-section, where a reduction of the photoemission cannot be explained by a thickness variation. We also investigate the laser-induced damage on P1 patterning lines performed after the deposition of CIGS. We then document, for the first time, the existence of a short-range damaged area, which is independent of the application of an optical aperture on the laser path. Our findings pave the way for a better understanding of P1-induced power losses and introduce new insights into the improvement of current strategies for industry-relevant module interconnection schemes.
CRIS-Team Scopus Importer:2020-08-14
Keywords: Cell-to-module efficiency gap; CIGS; Hyperspectral photoluminescence; Laser ablation short-range heat effect; P1-induced power losses

Deciphering the Role of Impurities in Methylammonium Iodide and Their Impact on the Performance of Perovskite Solar Cells - Levchuk, Ievgen; Hou, Yi; Gruber, Marco; Brandl, Marco; Herre, Patrick; Tang, Xiaofeng; Högl, Florian; Batentschuk, Miroslaw; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Tykwinski, Rik; et al. (Advanced Materials Interfaces, 2016)
Solution-based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, the purity levels of common perovskite precursor solutions have been investigated and a number of impurities that are critically important toward controlling the crystallization of perovskites are found. In this study, an in-depth chemical study of the possible impurities formed during CHNHI preparation is presented and their relevance on solar cell processing is revealed. A primary consideration is the chemical transformation of hypophosphorous acid, which plays the role of the stabilizer for HI. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity-free precursors versus precursors containing different concentrations of impurities. Most interestingly, it is revealed that a certain concentration of impurities is detrimental to the growth of large-grained crystals. PbHPO nanoparticles, which are formed after hypophosphorous acid transformation, actually cause crystal domain growth through serving as a nucleation center. This study gives valuable insight into the rate determining steps of perovskite crystal growth and further provides the basis for developing reliable and reproducible high-performance recipes for perovskite solar cell processing.
Keywords: Grain size; Impurities; Perovskites; Seed growth; Solar cells

Deep electronic levels in n-type and p-type 3C-SiC - Schöler, Michael; Lederer, Maximilian; Wellmann, Peter (Materials Science Forum, 2019)
In recent times, 3C-SiC is gaining more and more interest in terms of applications for optoelectronics and quantum computing. Cubic SiC exhibits a number of luminescent defects in the near infrared originating from deep electronic levels. Temperature dependent photoluminescence measurements were conducted on n-type and p-type 3C-SiC in order to investigate the formation of dopant related point defects as well as intrinsic point defects and defect complexes. The results indicate a number of VSi, VC and VCCSi related defects which might be suitable candidates for future optoelectronic applications.
CRIS-Team Scopus Importer:2019-09-17
Keywords: 3C-SiC; Carbon vacancy; Defects; Doping; P-type; Sublimation growth

Deep Learning-based Pipeline for Module Power Prediction from EL Measurements - Hoffmann, Mathis; Buerhop-Lutz, Claudia; Reeb, Luca; Pickel, Tobias; Winkler, Thilo; Doll, Bernd; Würfl, Tobias; Peters, Ian Marius; Brabec, Christoph; Maier, Andreas; Christlein, Vincent (Progress in Photovoltaics: Research and Applications, 2021)
Automated inspection plays an important role in monitoring large-scale photovoltaic power plants. Commonly, electroluminescense measurements are used to identify various types of defects on solar modules but have not been used to determine the power of a module. However, knowledge of the power at maximum power point is important as well, since drops in the power of a single module can affect the performance of an entire string. By now, this is commonly determined by measurements that require to discontact or even dismount the module, rendering a regular inspection of individual modules infeasible. In this work, we bridge the gap between electroluminescense measurements and the power determination of a module. We compile a large dataset of 719 electroluminescense measurementsof modules at various stages of degradation, especially cell cracks and fractures, and the corresponding power at maximum power point. Here,we focus on inactive regions and cracks as the predominant type of defect. We set up a baseline regression model to predict the power from electroluminescense measurements with a mean absolute error of 9.0+/-3.7W (4.0+/-8.4%). Then, we show that deep-learning can be used to train a model that performs significantly better (7.3+/-2.7W or 3.2+/-6.5%). With this work, we aim to open a new research topic. Therefore, we publicly release the dataset, the code and trained models to empower other researchers to compare against our results. Finally, we present a thorough evaluation of certain boundary conditions like the dataset size and an automated preprocessing pipeline for on-site measurements showing multiple modules at once.

Defect etching of non-polar and semi-polar faces in SiC - Sakwe, Aloysius; Jang, Yeon-Suk; Wellmann, Peter (Materials Science Forum, 2007)
Wet chemical etching using molten KOH is the most frequently applied method to reveal structural defects in SiC. Until now etching kinetics of SiC in planes different from the polar c-plane has not been reported. In this paper we report on defect etching of SiC in non-polar faces. Using a calibrated KOH defect-etching furnace with possibilities to set accurate etching temperatures we have etched SiC samples of various orientations to (i) study defect occurrence and their morphologies (ii) set KOH defect etching parameters for SiC for these orientations and (iii) investigate etching kinetics in relation to anisotropy/surface polarity. For non-polar planes of the same orientations a comparison in etching kinetics and defect morphologies in crystals grown in different directions is presented.
Keywords: etching; surface polarity; surface potential; activation energy; etching kinetics

Defect recognition in crystalline silicon solar cells by X-ray tomosynthesis with layer resolution - Voland, Virginia; Hoyer, Ulrich; Auer, Richard; Salamon, Michael; Uhlmann, Norman; Brabec, Christoph (Progress in Photovoltaics: Research and Applications, 2015)
The increasing demand for higher quality in solar cell production led to the development of several inline control methods. Beneath the image-guided methods, X-ray is not yet very well investigated for the application in photovoltaic research but shows high potential. In contrast to the ordinary X-ray radioscopic method, the tomosynthesis technique exhibits additional depth information of the solar cells and modules. In this article, several applications of tomosynthesis for the investigation of solar cells and modules are studied. It will be shown what potential the application of X-ray and especially tomosynthesis has as quality control tool for photovoltaics.
Keywords: Defect recognition; Metrology; Tomosynthesis; X-ray

Defects and performance of Si PV modules in the field - an analysis - Denz, J.; Hepp, Johannes; Buerhop, C.; Doll, Bernd; Hauch, J.; Brabec, Christoph; Peters, I. M. (Energy and Environmental Science, 2022)
Photovoltaic installations will likely become one of the major power sources in the 21st century and we need photovoltaic modules to operate reliably. In this review, we explore what is known today about the status of installed crystalline silicon photovoltaic modules in the world, how different sources classify module defects, and what we might deduce for future installations. Looking at more than 200 results from 132 installations and 79 reports, we find that PV modules in general are robust in outdoor operation, with about one in 250 modules failing completely each year. About one in ten modules will develop a defect resulting in greater than expected power loss throughout their lifetime, and practically every module will develop visually perceivable alterations. We observe no trends of changes over time in these findings, hence there is no indication that future performance will deviate dramatically. We note though that more information is needed. Available studies represent a module fleet with greater age than current installations, and are over-representing multicrystalline - compared to monocrystalline silicon, and AL-BSF - compared to PERC cell architectures. Studies from Asia and Africa and from tropical climates are underrepresented. A major challenge in the analysis was the variety of metrics used. To facilitate easier comparison, we propose reporting guidelines.
CRIS-Team WoS Importer:2022-05-13

Defect structures at the silicon/3C-SiC interface - Hens, Philip; Müller, Julian; Spiecker, Erdmann; Wellmann, Peter (Materials Science Forum, 2012)
In all heteroepitaxial systems the interface between substrate and layer is a crucial point. In this work SEM and TEM studies on the interface between silicon substrate and cubic silicon carbide (3C-SiC) layers obtained by chemical vapor deposition (CVD) are presented. A clear connection between process parameters, like the design of substrate cleaning, and the heating ramp, and resulting defect structures at the substrate-layer interface could be found. Whereas the process step of etching in hot hydrogen for oxide removal is crucial for avoiding the generation of closed voids of type 2, the design of the temperature ramp-up to growth temperature during carbonization influences the interface roughness. Here a fast ramp helps to obtain a flat interface. © (2012) Trans Tech Publication
Keywords: Cubic silicon carbide; Dislocations; Heteroepitaxy; Interface; Roughness; Voids

Deformation Mechanisms in Compositionally Complex Polycrystalline CoNi-Base Superalloys: Influence of Temperature, Strain-Rate and Chemistry - Bezold, Alexander; Freund, Lisa; Förner, Andreas; Völkl, Johannes; Huber, Laura-Kristin; Göken, Mathias; Neumeier, Steffen (Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, 2022)
Recent studies revealed the excellent high temperature properties of polycrystalline CoNi-base superalloys. However, their underlying deformation behavior has been reported only scarcely so far. In this work, the deformation mechanisms of four polycrystalline compositionally complex CoNi-base superalloys with slightly varying chemical compositions were investigated by compression and creep experiments at temperatures between 750 degrees C and 850 degrees C and strain-rates between 10 (3) and 10 (8) s(-1). In the two (Ta + Ti)-rich alloys, a transition of the deformation mechanism from shearing by APB-coupled dislocation pairs to stacking fault shearing and finally also to microtwinning is observed with decreasing strain-rate and increasing temperature. In contrast, APB-based shearing mechanisms represent the dominant mechanism in both (Al + W)-rich alloys in all conditions. At high temperatures and low strain-rates, dislocation glide-climb processes also contribute to plastic deformation in all alloys. By correlating the underlying defect structures with the mechanical properties of these alloys, it becomes evident that a transition to stacking fault shearing and microtwinning leads to a lower strain-rate dependency and superior high-temperature strength in comparison with APB-based mechanisms. Reasons for the different deformation mechanisms, the influence of segregation processes, the consequences for mechanical properties and implications for a mechanism-based alloy design are discussed.
CRIS-Team WoS Importer:2023-01-06

Degradable bone substituition material based on cellular Ca-phosphates - Götz-Neunhoeffer, Friedlinde; Göbbels, Matthias; Enderle, Ralph; Neubauer, Jürgen; Zeschky, Jürgen (Applied Mineralogy, 2004)
UnivIS-Import:2015-04-16:Pub.2004.nat.dgeo.IGM.LM.degrad

Degradation through Directional Self-Doping and Homogeneous Density of Recombination Centers Hindered by 1,8-Diiodooctane Additive in Non-Fullerene Organic Solar Cells - Almora, Osbel; Wiegand, Julius; Lopez-Varo, Pilar; Matt, Gebhard J.; Brabec, Christoph (Solar RRL, 2021)
Non-fullerene-based organic solar cells (OSCs) have recently proven to perform with efficiencies above 18%. This is an important milestone for one of the most promising technologies in the fields of flexible and transparent/semitransparent photovoltaics. However, the stability of OSCs is still a challenging issue to meet the industry requirements. Herein, several devices with IT-4F:PM6 as the active layer with and without 1,8-Diiodooctane (DIO) additive are characterized before and after a 1400 h degradation test under 1 sun white light-emitting diode (LED) illumination intensity. The optoelectronic study via impedance spectroscopy under illumination at quasi-open-circuit correlates the use of DIO as an additive with a retarded degradation behavior and an overall improved device performance. In dark conditions, the Mott-Schottky analysis suggests that samples without DIO develop self-doping during degradation, changing the p-i-n doping profile into a p-n type, most likely related to the evolution of the blend demixing. These mechanisms are further confirmed by drift-diffusion simulations. Space-oriented redistribution of shallow trap levels (self-doping) and homogeneous increase in deep-trap levels (nonradiative recombination) are shown to be hindered by the use of the DIO additive.
CRIS-Team WoS Importer:2021-03-19

Delocalisation softens polaron electronic transitions and vibrational modes in conjugated polymers - Kahmann, Simon; Loi, Maria A.; Brabec, Christoph (Journal of Materials Chemistry C, 2018)
In this work we study the photoinduced signatures of polarons in conjugated polymers and the impact of charge carrier delocalisation on their spectra. The variation of film crystallinity for two prototypical systems – blends of the homopolymer P3HT or the donor–acceptor polymer PCPDTBT with PCBM – allows probing changes of the polaron absorption in the mid infrared spectral region. Increased polaron delocalisation entails a shift of the electronic transition to lower energy in both cases. Also, infrared active vibrations soften due to a higher polymer chain order. Our findings help in providing a more complete understanding of polaron properties in conjugated materials and bring the application of the polaron absorption spectrum as an indicator for the environment on a more thoroughly studied foundatio

Delocalization of exciton and electron wavefunction in non-fullerene acceptor molecules enables efficient organic solar cells - Zhang, Guichuan; Chen, Xian Kai; Xiao, Jingyang; Chow, Philip C.Y.; Ren, Minrun; Kupgan, Grit; Jiao, Xuechen; Chan, Christopher C.S.; Du, Xiaoyan; Xia, Ruoxi; Chen, Ziming; Yuan, Jun; et al. (Nature Communications, 2020)
A major challenge for organic solar cell (OSC) research is how to minimize the tradeoff between voltage loss and charge generation. In early 2019, we reported a non-fullerene acceptor (named Y6) that can simultaneously achieve high external quantum efficiency and low voltage loss for OSC. Here, we use a combination of experimental and theoretical modeling to reveal the structure-property-performance relationships of this state-of-the-art OSC system. We find that the distinctive π–π molecular packing of Y6 not only exists in molecular single crystals but also in thin films. Importantly, such molecular packing leads to (i) the formation of delocalized and emissive excitons that enable small non-radiative voltage loss, and (ii) delocalization of electron wavefunctions at donor/acceptor interfaces that significantly reduces the Coulomb attraction between interfacial electron-hole pairs. These properties are critical in enabling highly efficient charge generation in OSC systems with negligible donor-acceptor energy offset.
CRIS-Team Scopus Importer:2020-08-14

Dependence of the seed layer quality on different temperature ramp-up conditions for 3C-SiC hetero-epitaxy on Si (100) - Hens, Philip; Wagner, G.; Hölzing, Astrid; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2012)
Usually a waiting step at around 1000 degrees C to 1100 degrees C is implemented during the carbonization for 3C-SiC epitaxy on silicon in order to form a closed carbon layer which prevents the formation of voids by evaporation of Si. On the other hand, such a process step may lead to non-ideal nucleation conditions resulting in a low layer quality with high densities of defects and domain boundaries. Our investigations indicate that a continuous temperature ramp-up with the highest possible heating rate and no waiting step is preferable and results in an improved layer quality concerning domain sizes as confirmed by X-ray diffraction measurements of the full width at half maximum of the SiC(200) reflection. The result can be understood within the framework of the Tammann theory for the temperature dependence of nucleation and growth. The two thermal regimes, as proposed by Tammann, had been located at temperatures of around 1000-1100 degrees C for nucleation and > 1200 degrees C for growth. (C) 2011 Elsevier B. V. All rights reserved.
Keywords: Growth models; Chemical vapor deposition processes; Inorganic compounds; Semiconducting silicon compounds; Cubic silicon carbide; Heteroepitaxy

Depth-resolved and temperature-dependent analysis of phase formation mechanisms in selenized Cu-Zn-Sn precursors by Raman spectroscopy - Stroth, Christiane; Sayed, Mohamed H.; Schuster, Matthias; Ohland, Joerg; Hammer-Riedel, Ingo; Hammer, Maria S.; Wellmann, Peter; Parisi, Jürgen; Gütay, Levent (Journal of Materials Science: Materials in Electronics, 2016)
We present a study on the temperature and film depth dependent phase formation in Cu-Zn-Sn-Se thin films. Zn/Sn/Cu precursors were selenized at different temperatures, followed by depth-resolved Raman profiling. A high depth resolution for Raman analysis was achieved by a special sample preparation step using a focused ion beam to prepare shallow angle cross sections (SACS) of the absorber. Multi-phase structures were observed at low selenization temperatures with a first formation of the quaternary CuZnSnSe at only 250 °C and the existence of SnO in films annealed at 330 °C. At high selenization temperatures up to 560 °C CuZnSnSe was the main phase with some traces of ZnSe and a MoSe interface layer at the back contact. Furthermore, compositional gradients were investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy measurements on sample cross sections. The combination of these results allows for observation of both elemental composition and phase composition of the films and their dynamics during the annealing procedur
Keywords: CZTSe; kesterite; Raman depth profiling; secondary phase formation; thin film solar cells

Depth-resolved and temperature dependent analysis of phase formation processes in Cu–Zn–Sn–Se films on ZnO substrates - Stroth, Christiane; Sayed, Mohamed H.; Schuster, Matthias; Ohland, Joerg; Hammer-Riedel, Ingo; Hammer, Maria S.; Wellmann, Peter; Parisi, Jürgen; Gütay, Levent (Journal of Materials Science: Materials in Electronics, 2017)
The constitution of secondary phases in kesterite CuZnSnSe (CZTSe) thin films is still a limiting factor for their application in solar cells. Therefore an enhanced understanding of phase formation processes during the fabrication of CZTSe films is required. In this study we present a temperature and film-depth dependent phase analysis of Zn/Sn/Cu precursors on ZnO substrates selenized at different temperatures. A special sample preparation step using a focused ion beam was applied to prepare shallow angle cross sections for depth-resolved Raman profiling of the thin films. At low selenization temperatures multiphase structures are demonstrated and a first formation of CZTSe besides secondary phases at only 250 °C is detected. At high selenization temperatures an accumulation of ZnSe at the interface of CZTSe and ZnO substrates is observed. Furthermore indications for the formation of a thin SnO interface layer were found by X-ray diffraction, secondary electron microscopy and energy dispersive X-ray spectrometr
Keywords: kesterite; phase formation; solar cells

Design, development and characterization of graphene sand nano-composite for water filtration - Abro, Shahid Hussain; Chandio, Alidad; Alaboodi, Abdulaziz S.; Channa, Iftikhar Ahmed (Pakistan Journal of Scientific and Industrial Research Series A: Physical Sciences, 2020)
Water purification and filtration is a global issue and many researchers are engaged to resolve this problem by adopting the scientific approach, graphene sand composite was prepared through biosynthesized technique. River sand was used in this context to remove the impurities already present in the sand 0.1M nitric acid treated the sand and the product was powder black in colour, referred as GSC, graphene sand composite. SEM, XRD and FTIR characterization was used to analyze the results. SEM images showed nano sized layers or sheets of graphene extending outwards.The XRD peak represents the multi lagered graphene structure which is formed by the treatment of the composite with acid and application of the high temperature during experiment UV-visible spectroscopy results successfully reveals the filtration difference between mud water and filtered water.
CRIS-Team Scopus Importer:2020-11-06
Keywords: Biosynthesized; Graphene; Sand particles; Sugar anchoring; Water filtration

Designing ternary blend all-polymer solar cells with an efficiency of over 10% and a fill factor of 78% - Li, Zhenye; Ying, Lei; Xie, Ruihao; Zhu, Peng; Li, Ning; Zhong, Wenkai; Huang, Fei; Cao, Yong (Nano Energy, 2018)
In recent years, ternary blend bulk-heterojunction (BHJ) all-polymer solar cells have been gradually developed to better utilize the solar irradiance spectrum. However, power conversion efficiencies remain below 10%, mainly because of the low fill factor. Generally, the fill factor of all-polymer solar cells is limited mainly by the competition between the recombination and extraction of free charges. Here, we design advanced ternary blend all-polymer solar cells with a high fill factor of 78%, thus demonstrating how such recombination thresholds can be overcome. These results can be attributed to the high and balanced bulk charge mobility, reduced recombination, and optimized morphology, as well as the intimate mixing properties of the two donors in the photoactive layer.
Keywords: All-polymer solar cell; Ternary blend; Reduced recombination; Intimate mixing properties

Designing ternary blend bulk heterojunction solar cells with reduced carrier recombination and a fill factor of 77% - Gasparini, Nicola; Jiao, Xuechen; Heumüller, Thomas; Baran, Derya; Matt, Gebhard; Fladischer, Stefanie; Spiecker, Erdmann; Ade, Harald; Brabec, Christoph; Ameri, Tayebeh (Nature Energy, 2016)
In recent years the concept of ternary blend bulk heterojunction (BHJ) solar cells based on organic semiconductors has been widely used to achieve a better match to the solar irradiance spectrum, and power conversion effciencies beyond 10% have been reported. However, the fill factor of organic solar cells is still limited by the competition between recombination and extraction of free charges. Here, we design advanced material composites leading to a high fill factor of 77% in ternary blends, thus demonstrating how the recombination thresholds can be overcome. Extending beyond the typical sensitization concept, we add a highly ordered polymer that, in addition to enhanced absorption, overcomes limits predicted by classical recombination models. An effective charge transfer from the disordered host system onto the highly ordered sensitizer effectively avoids traps of the host matrix and features an almost ideal recombination behaviour.

Design of donor-acceptor star-shaped oligomers for efficient solution-processible organic photovoltaics - Ponomarenko, S. A.; Luponosov, Y. N.; Min, Jie; Solodukhin, A. N.; Surin, N. M.; Shcherbina, M. A.; Chvalun, S. N.; Ameri, Tayebeh; Brabec, Christoph (Faraday Discussions, 2014)
This contribution describes recent progress in the design, synthesis and properties of solution-processible star-shaped oligomers and their application in organic photovoltaics. Even though alternative chemistry has been used to design such oligomers, the most successful approach is based on a triphenylamine donor branching center, (oligo)thiophene conjugated spacers and dicyanovinyl acceptor groups. These are mainly amorphous low band-gap organic semiconductors, though crystalline or liquid crystalline ordering can sometimes be realized. It was shown that the solubility, thermal behavior and structure of such molecules in the bulk strongly depend on the presence and position of alkyl groups, as well as on their length. The photovoltaic properties of solution-processed molecules of this type are now approaching 5% which exceeds those of vacuum-sublimed devices. The design rules and future perspectives of this class of organic photovoltaic molecules are discussed.

Design of Highly Efficient Semitransparent Perovskite/Organic Tandem Solar Cells - Rossi, Daniele; Forberich, Karen; Matteocci, Fabio; Der Maur, Matthias Auf; Egelhaaf, Hans-Joachim; Brabec, Christoph; Di Carlo, Aldo (Solar RRL, 2022)
Solar cells transparent in the visible range are highly requested for integration in see-through photovoltaic (PV) applications such as building glass façades or greenhouse roofs. The development of advanced transparent PV can fully exploit the tandem technology where the top cell absorbs the near-ultraviolet solar spectrum while the bottom one absorbs the near-infrared part. Herein, a possible implementation of this tandem PV paradigm, namely, the tandem structure composed of a high-bandgap halide perovskite solar cell and a low-bandgap organic solar cell, is considered. Electro-optical simulation results based on parameters calibrated on experimental data show that an efficiency of 15% can be achieved with an average visible transmittance above 50%. This can be obtained considering the halide perovskite with mixed chlorine and bromine anions, a nonfullerene-based bulk heterojunction, a well-calibrated light management, and a three-terminal configuration of the tandem.
CRIS-Team Scopus Importer:2022-07-08
Keywords: organic solar cells; pervoskite solar cells; solar cell simulations; tandem perovskite/organic solar cells; transparent solar cells

Design of low band gap small molecules with alkyldicyanovinyl acceptor and different donor groups for efficient bulk heterojunction organic solar cells - Luponosov, Yuriy N.; Min, Jie; Solodukhin, Alexander N.; Chvalun, Sergei N.; Ameri, Tayebeh; Brabec, Christoph; Ponomarenko, Sergey A. (2015 Organic Photovoltaics XVI, 2015)
A library of low band gap small molecules with alkyldicyanovinyl acceptor and triphenylamine, tris(2-methoxyphenyl)amine or dithienosilole donor groups linked through (oligo)thiophene conjugated spacers was designed and successfully synthesized. Systematic variations of the alkyl chain length and the number of conjugated thiophene rings in the molecules allowed to elucidate the structure-properties relationships for their solubility, absorption spectra, phase behavior, morphology and structure in thin films, as well as photovoltaic properties. Bulk heterojunction organic solar cells prepared from these molecules as donors and PCBM[70] as acceptor by solution processing showed power conversion efficiency up to 5.4-6.4%.
Keywords: bulk heterojunction; dicyanovinyl; dithienosilole; donor-acceptor oligomers; oligothiophenes; Organic photovoltaics; solution processing; triphenylamine

Design of the solution-processed intermediate layer by engineering for inverted organic multi junction solar cells - Li, Ning; Stubhan, Tobias; Baran, Derya; Min, Jie; Wang, Haiqiao; Ameri, Tayebeh; Brabec, Christoph (Advanced Energy Materials, 2013)
An equivalent ohmic contact is successfully formed between low-conductivity poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) and solution-processed aluminum-doped ZnO (AZO). Because of its promising optical and electrical properties, this combination can serve as an efficient interconnection layer as well as an optical spacer in inverted-structure organic tandem devices. © 2013 WILEY-VCH Verlag GmbH & Co.
Keywords: Aluminum-doped ZnO; Interconnection layers; Intermediate layers; Multi junction solar cells; Optical and electrical properties; Poly(3; 4-ethylenedioxythiophene):poly(styrenesulfonate); Solution-processed; Tandem devices Engineering controlled terms: Conducting polymers; Ohmic contacts; Zinc oxide Engineering main heading: Electric properties

Detailed optical modelling and light-management of thin-film organic solar cells with consideration of small-area effects - Lipovšek, Benjamin; Čampa, Andrej; Guo, Fei; Brabec, Christoph; Forberich, Karen; Krč, Janez; Topič, Marko (Optics Express, 2017)
We present detailed numerical and experimental investigation of thin-film organic solar cells with a micro-textured light management foil applied on top of the front glass substrate. We first demonstrate that measurements of small-area laboratory solar cells are susceptible to a significant amount of optical losses that could lead to false interpretation of the measurement results. Using the combined optical model CROWM calibrated with realistic optical properties of organic films and other layers, we identify the origins of these losses and quantify the extent of their influence. Further on, we identify the most important light management mechanisms of the micro-textured foil, among which the prevention of light escaping at the front side of the cell is revealed as the dominant one. Detailed three-dimensional simulations show that the light-management foil applied on top of a large-area organic solar cell can reduce the total reflection losses by nearly 60% and improve the short-circuit current density by almost 20%. Finally, by assuming realistic open-circuit voltage and especially the realistic fill factor that deteriorates as the absorber layer thickness is increased, we determine the optimal absorber layer thickness that would result in the highest power conversion efficiency of the investigated organic solar cells.
Keywords: Engineering controlled terms: Open circuit voltage; Optical films; Optical properties; Organic solar cells; Substrates; Thin film solar cells; Thin films Experimental investigations; Glass substrates; Light management; Optical modeling; Optical modelling; Power conversion efficiencies; Three dimensional simulations; Total reflection Engineering main heading: Solar cells

Detection of effective recombination centers in fluorescent SiC using thermally stimulated luminescence - Wei, Yi; Künecke, Ulrike; Wellmann, Peter; Ou, Haiyan (5th international workshop on LED and Solar Applications, 2017)
Two n-type 6H fluorescent SiC (f-SiC) samples have been characterized using thermally stimulated luminescence (TSL) spectroscopy, where the dominant carriers recombination regime has been found via the numerical simulations.<br
Keywords: 6H SiC; TSL; re-trapping

Detection of X-ray photons by solution-processed lead halide perovskites - Yakunin, Sergii; Sytnyk, Mykhailo; Kriegner, Dominik; Shrestha, Shreetu; Richter, Moses; Matt, Gebhard; Azimi, Hamed; Brabec, Christoph; Stangl, Julian; Kovalenko, Maksym V.; Heiß, Wolfgang (Nature Photonics, 2015)
The evolution of real-time medical diagnostic tools such as angiography and computer tomography from radiography based on photographic plates was enabled by the development of integrated solid-state X-ray photon detectors made from conventional solid-state semiconductors. Recently, for optoelectronic devices operating in the visible and near-infrared spectral regions, solution-processed organic and inorganic semiconductors have also attracted a great deal of attention. Here, we demonstrate a possibility to use such inexpensive semiconductors for the sensitive detection of X-ray photons by direct photon-to-current conversion. In particular, methylammonium lead iodide perovskite (CH3NH3PbI3) offers a compelling combination of fast photoresponse and a high absorption cross-section for X-rays, owing to the heavy Pb and I atoms. Solution-processed photodiodes as well as photoconductors are presented, exhibiting high values of X-ray sensitivity (up to 25 μC mGyair-1 cm-3) and responsivity (1.9 × 104 carriers/photon), which are commensurate with those obtained by the current solid-state technology.
Keywords: Engineering controlled terms: Chemical detection; Diagnosis; Diagnostic radiography; Infrared devices; Lead; Optoelectronic devices; Perovskite; Photons; Single crystals; Solid state device structures Absorption cross sections; Inorganic semiconductors; Medical diagnostic tools; Sensitive detection; Solid state semiconductors; Solid state technology; Solution-processed; Visible and near infrared Engineering main heading: X ray radiography

Determination of charge carrier concentration in n- and p-doped SiC based on optical absorption measurements - Weingärtner, Roland; Wellmann, Peter; Bickermann, Matthias; Hofmann, Heinz-Dieter; Straubinger, Thomas; Winnacker, Albrecht (Applied Physics Letters, 2002)
We have investigated the effect of doping on absorption for various SiC polytypes, i.e., n-type (N) 6H-SiC, 4H-SiC, and 15R-SiC, p-type (Al) 6H-SiC, and 4H-SiC, and p-type (B) 6H-SiC. For these polytypes the band-gap narrowing with higher doping concentration is observed. In addition, for n-type doping below band-gap absorption bands at 464 nm for 4H-SiC, at 623 nm for 6H-SiC, and at 422 and 734 nm for 15R-SiC are observed. The peak intensities of these absorption bands show a linear relation to the charge carrier concentration obtained from Hall measurements. The corresponding calibration factors are given. As an application a purely optical wafer mapping of the spatial variation of the charge carrier concentration is demonstrated. (C) 2002 American Institute of Physics.
Keywords: SiC; absorption; charge carrier concentration; Hall; mapping

Determination of dislocation density in GaN layers using KOH defect MOVPE grown etching - Wellmann, Peter; Sakwe, Aloysius; Oehlschläger, Felix; Hoffmann, Veit; Zeimer, Ute; Knauer, Arne (Journal of Crystal Growth, 2008)
We report on molten KOH-based defect etching of GaN epitaxial layers for the quantitative determination of the dislocation density. Etching process parameters were established at 450 degrees C that are suitable to reveal threading edge and threading screw dislocations at the same time and, hence, allow for the quantitative determination of the total dislocation density in the metal organic vapor-phase epitaxy (MOVPE) grown GaN layers. The determined dislocation numbers in the 10(8)cm(-2) range are correlated (i) with the full-width half-maximum of rocking curves of the (3 0 (2) over bar) reflection and (ii) dark spots observed by cathodoluminescence of the etched GaN surfaces. (C) 2007 Elsevier B.V. All rights reserved.
Keywords: Defect etching; GaN; KOH

Determination of doping levels and their distribution in SiC by optical techniques - Wellmann, Peter; Weingärtner, Roland (Materials Science and Engineering B-Advanced Functional Solid-State Materials, 2003)
We review an absorption measurement based characterization method for the determination of doping levels and doping level distribution in SiC which is quantitative and serves all the advantages of optical techniques like being non-contact, non-destructive and quick. Calibration plots for the important SiC polytypes 4H-SiC and 6H-SiC, both n- and p-type, have been determined in the technological relevant charge carrier concentration range of 10(17)-10(19) cm(-3). The underlying physical phenomena of the measurement technique as well as the experimental setup and its precision will be discussed. Several absorption mappings will be shown in order to demonstrate the potential of the presented method as research as well as industrial quality testing tool of SiC wafers. In an outlook the application of the method for other semiconductor materials like GaAs will be discussed. (C) 2003 Elsevier B.V. All rights reserve
Keywords: Silicon carbide; Doping; Characterization; Absorption mapping

Determination of exciton capture cross-sections of neutral nitrogen donor on cubic and hexagonal sites in n-type (N) 6H-SiC - Weingärtner, Roland; Albrecht, A.; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2003)
The dopant concentration dependence of the zero phonon lines of the nitrogen bound excitons in n-type (N) 6H-SiC in high resolution low temperature photoluminescence spectra are investigated. The asymmetric line broadening of the zero phonon lines is interpreted in terms of overlapping wave functions. From the change of the ratio of the hexagonal zero phonon lines to the cubic zero phonon lines as a function of charge carrier concentration the capture cross sections of neutral nitrogen donors for excitons were determined to be (44.5 Angstrom)(2)pi and (33.5 Angstrom)(2)pi on hexagonal and cubic lattice site, respectivel
Keywords: Bound Exciton; Exciton Tails; Lattice Site; Nitrogen Donor; Photoluminescence (PL)

Determination of GaN solubility in supercritical ammonia with NH4F and NH4Cl mineralizer by in situ x-ray imaging of crystal dissolution - Schimmel, Saskia; Lindner, Michael; Steigerwald, Thomas; Hertweck, Benjamin; Richter, Theresia M.M.; Künecke, Ulrike; Alt, Nicolas; Niewa, Rainer; Schlücker, Eberhard; Wellmann, Peter (Journal of Crystal Growth, 2015)
Quantitative data on the solubility of GaN in supercritical ammonia using NH4F as mineralizer are reported. The solubility is determined by in situ x-ray imaging of the dissolution of GaN single crystals. First, solubility values obtained by this method with NH4Cl as mineralizer are presented and discussed with respect to existing literature data Monitoring the dissolution process in situ reveals the time when the solubility limit is reached. Thus, it allows to distinguish the saturation of the solution from dissolution based on mass transport and deposition. This is a key advantage of solubility measurements by in situ x-ray imaging compared to gravimetric methods. Our results indicate that the solubility limit is reached much faster than usually assumed in gravimetric solubility studies and the solubility of GaN in ammonothermal media is significantly lower than reported so far. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: Solubility; Solvents; Mineralizers; Growth from solutions; Ammonothermal crystal growth; Nitrides

Determination of material inhomogeneities in CuIn(Se,S)(2) solar cell materials by high resolution cathodoluminescence topography - Oehlschläger, Felix; Müller, Julian; Künecke, Ulrike; Hoelzing, Astrid; Schurr, Roland; Hock, Rainer; Wellmann, Peter (Energy Procedia, 2010)
CIS based polycrystalline semiconductors are used for thin film solar cells in laboratory and industry. Nevertheless, even for highly efficient absorbers from different growth techniques, these films are reported to contain inhomogeneities from nanometer to millimeter scale. In this paper we have analyzed inhomogeneities on a sub-mu m scale of CuIn(Se,S)(2) solar cell absorber materials processed by annealing of elemental layer precursors using high spatial resolution cathodoluminescence mapping. The measurements were carried out in a scanning electron microscope which has cathodoluminescence (CL) and energy dispersive x-ray fluorescence (EDX) capabilities to study materials composition. Cathodoluminescence from CuIn(Se,S)(2) at energies around 0.9 eV to 1.2 eV was detected by a spectrometer with a cooled InGaAs photo diode array. For better luminescence signals, the samples were cooled down to 80K (liquid nitrogen). From the energetic position of the cathodoluminescence peaks we have deduced the varying CuIn(Se,S)(2) materials composition. EDX measurements were carried out to verify the CL. (C) 2010 Published by Elsevier L
Keywords: Cathodoluminescence; CL; Energy dispersive x-ray; EDX; thin film; absorber; CuIn(S; Se); topography; mapping

Determination of phase diagrams of binary and ternary organic semiconductor blends for organic photovoltaic devices - Li, Ning; Machui, Florian; Waller, David; Koppe, Markus; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2011)
Ternary blends were recently suggested as a sound approach to increase the short circuit current density of organic solar cells by sensitizing the bulk heterojunction (BHJ) with a further absorber, i.e., a low band gap polymer. Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b́]dithiophene) -alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) is a suitable candidate as low band gap polymer for ternary blends with poly(3-hexylthiophene) (P3HT) and [6,6]-pheny-C-butyric acid methyl ester ([60]PCBM) due to its ideal energy level and charge carrier properties. Phase diagrams are common in polymer science to visualize the mixing behavior of multicomponent systems as a function of temperature. In this study, we have used differential scanning calorimetry (DSC) to extract phase diagrams for binary and ternary organic semiconductor blends, and built the corresponding solar cells to analyze correlations between the thermal and the electrical properties of such semiconductor blends. © 2011 Elsevier B.V. All rights reserved.
Keywords: Differential scanning calorimetry (DSC); Organic photovoltaic devices; P3HT/PCBM/PCPDTBT; Phase diagram; Ternary blends

Determination of site occupancy of boron in 6H-SiC by multiple-wavelength neutron holography - Hayashi, Kouichi; Lederer, Maximilian; Fukumoto, Yohei; Goto, Masashi; Yamamoto, Yuta; Happo, Naohisa; Harada, Masahide; Inamura, Yasuhiro; Oikawa, Kenichi; Ohoyama, Kenji; Wellmann, Peter (Applied Physics Letters, 2022)
The local structure around boron doped in 6H-type silicon carbide (SiC) was investigated using neutron holography. Three-dimensional atomic images reconstructed from multiple-wavelength holograms revealed the boron substitution for both silicon and carbon. To determine boron locations accurately, we calculated holograms with varying occupancies of six different sites and fit image intensities with those obtained from experimental holograms by the steepest descent method. As a result, it was found that boron atoms were selectively located at the Si-C-cubic site layer. Furthermore, boundaries right above the boron locations were suggested from the absence of atomic images in the upper region of reconstruction.
CRIS-Team Scopus Importer:2022-04-22

Determination of solubility parameters for organic semiconductor formulations - Machui, Florian; Abbott, Steven; Waller, David; Koppe, Markus; Brabec, Christoph (Macromolecular Chemistry and Physics, 2011)
The concept of Hansen solubility parameters (HSP) is applied to organic semiconductors in order to determine and predict their solubility behavior, which is essential for the design of functional and environmentally friendly ink formulations for organic photovoltaics. Two different conjugated polymers, one semicrystalline and one dominantly amorphous, and one fullerene derivative are selected as prototype candidates to evaluate the applicability of the HSP concept for organic semiconductors. The method for determining the solubility parameters is described and the quality of the HSP fits as well as their suitability for designing of organic electronic inks are discussed in detail. The applicability of Hansen solubility parameters in designing organic semiconductor ink formulations is analyzed by determining and predicting the solubility behavior of three different organic semiconductors. A large number of solvents are studied and temperature-dependent solubility is examined to enhance the practical relevance of this work. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: conjugated polymers; fullerenes; Hansen solubility parameters (HSP); ink formulations; organic photovoltaics

Determination of the complex refractive index of powder phosphors - Solodovnyk, Anastasiia; Riedel, Daniel; Lipovšek, Benjamin; Osvet, Andres; Gast, Jessica; Stern, Edda; Forberich, Karen; Batentschuk, Miroslaw; Krč, Janez; Topič, Marko; Brabec, Christoph (Optical Materials Express, 2017)
We demonstrate a novel 2-step method to precisely determine both n and k of phosphors, luminescent inorganic particles, in the visible spectrum. To measure n we modified the Becke Line immersion method and verified its applicability in the absorption/ emission regions of phosphor particles (step 1). Particles were then embedded into a transparent binder and coated in thick layers (100-500 μm) on glass. Absorptance of the layers was measured with a novel approach: spectral angular resolved measurements. This method delivers accurate results by avoiding any errors from intense scattering inside the layers. A computational model was employed to extract k of particles from the measured absorptance data taking into account luminescence, scattering and re-absorption (step 2). The entire method was verified on reference materials. Finally, based on the proposed method, we determined in a broad wavelength range the n and k parameters for a variety of commonly used phosphors with few or no earlier reports on their n and k values (the complete set of numerical data is fully disclosed in the supplementary materials). © 2017 Optical Society of America.
Keywords: Light emission; Luminescence; Phosphors; Refractive index; Complex refractive index; Computational model; Immersion method; Inorganic particles; Phosphor particles; Powder phosphors; Reference material; Wavelength ranges; Numerical methods

Determination of the Electronic Energy Levels of Colloidal Nanocrystals using Field-Effect Transistors and Ab-Initio Calculations - Bisri, Satria Zulkarnaen; Degoli, Elena; Spallanzani, Nicola; Krishnan, Gopi; Kooi, Bart Jan; Ghica, Corneliu; Yarema, Maksym; Heiß, Wolfgang; Pulci, Olivia; Ossicini, Stefano; Loi, Maria Antonietta (Advanced Materials, 2014)
Colloidal nanocrystals electronic energy levels are determined by strong size-dependent quantum confinement. Understanding the configuration of the energy levels of nanocrystal superlattices is vital in order to use them in heterostructures with other materials. A powerful method is reported to determine the energy levels of PbS nanocrystal assemblies by combining the utilization of electric-double-layer-gated transistors and advanced ab-initio theory.
Keywords: ab-initio; colloidal nanocrystals; field-effect transistors; ionic liquid; quantum dots

Determination of the Molar Extinction Coefficient of Colloidal Selenium for Optical Characterization of Stabilized Nanoparticulate Dispersions - Schuster, Matthias; Wernicke, Tobias; Möckel, Stefan; Wellmann, Peter (International Journal of Nanoparticles and Nanotechnology, 2016)
To prepare fully printed copper-indium-diselenide solar-cell-absorbers it is necessary to have well defined and printable precursor-inks. In this work, the synthesis and different approaches for the colloidal stabilization of Selenium (Se) nanoparticles are presented, which should ultimately serve as a selenium source for CISe absorbers. The produced particles were stabilized with different concentrations of Polyvinylpyrrolidone (PVP) and micelles (TX100) respectively. The resulting suspensions were analyzed in aspect of particle size and colloidal stability using dynamic light scattering (DLS). It was shown, that both approaches lead to stable colloidal suspensions with ca. 80 - 100 nm particle size. The PVP stabilized suspension stays stable for four weeks at a Zeta potential of > 35 - 25 mV whereas the TX100 stabilized suspension was only short-time-stable due to loss in Zeta potential over time. UV/VIS spectroscopy and Lambert-Beer’s law were used to determine the concentration of Se in the dispersion. The molar extinction coefficient ε of colloidal selenium was calculated to be 1.44 × 10³ l/(mol·cm) for ε (Se) respectively 2.63 × 107 l/(mol·cm) for ε (Se-NP) ± 9 % in both cases.
Keywords: Printable nanoparticles; Colloidal selenium; Stabilization; Dynamic light scattering; Concentration; Molar extinction coefficient; UV/VIS

Determination of the P3HT:PCBM solubility parameters via a binary solvent gradient method: Impact of solubility on the photovoltaic performance - Machui, Florian; Langner, Stefan; Zhu, Xiangdong; Abbott, Steven; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2012)
We discuss an alternative route to determine the solubility parameters of two prototype organic semiconductors, namely the semi-crystalline polymer poly-(3-hexylthiophene-2,5-diyl) (P3HT) and the methano-fullerene derivative [6,6]-phenyl-C -butyric acid methyl ester (PCBM). The HSP (Hansen solubility Parameters) derived by this novel method are compared to the findings derived from the classical multi-solvent method to determine the HSP, and significantly higher accuracy is found. For this novel approach we designed two component solvent blend systems, being composed by mixing a solvent with a non-solvent. Varying the composition of the solvent non-solvent blends from 0% to 100% gradually converts a solvent into a non-solvent. This very accurate control of the dispersive, polar and hydrogen contributions to the overall solubility now allows determining the Hansen sphere for P3HT and PCBM with much higher accuracy. The transition from a solvent into a non-solvent was further followed by solar cell investigations. Comparing the solubility studies with device investigations allows identifying the processing limits of solvent systems. © 2012 Elsevier B.V. All rights reserved.
Keywords: Conjugated polymers; Fullerenes; Hansen solubility parameters; Ink formulations; Organic photovoltaics; Solvent blends

Determination of Thermal Properties of Carbon Materials above 2000 °C for Application in High Temperature Crystal Growth - Ihle, Jonas; Wellmann, Peter (Crystal Research and Technology, 2025)
This work reports on the determination of the heat conductivity of high temperature stable carbon materials in the temperature range well above 2000 °C where classic material characterization methods fail. Dense graphite (DG) materials as well as rigid and soft felt isolation (RFI/SFI) components have been investigated which are used during crystal growth of SiC by the physical vapor transport method (PVT) in the temperature regime of 2000 and 2400 °C. The applied materials characterization methods include low temperature physical heat conductivity measurements using laser flash analysis (LFA) in the temperature range 25–1200 °C, data extrapolation to elevated temperatures up to 2400 °C, and a correlation of heating processes and computer simulation of the temperature field of different hot zone designs. Using this approach, the calculated temperatures and experimentally determined values with an error of less than ± 2% at 2400 °C can be merged.
CRIS-Team Scopus Importer:2025-01-31
Keywords: carbon materials; high-temperature isolation; SiC PVT growth; temperature field simulation; thermal conductivity

Determining the coating speed limitations for organic photovoltaic inks - Jakubka, Florian; Heyder, Madeleine; Kaschta, Joachim; Machui, Florian; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2013)
To determine the output capability of present organic photovoltaic (OPV) materials, it is important to know the theoretical maximum coating speeds of the used semiconductor formulations. Here, we present a comprehensive investigation of the coating stability window of several prototype organic semiconductor inks relevant for organic solar cells. The coating stability window was first determined experimentally by a sheet to sheet coater at velocities of up to 10 m/min. A numerical simulation model based on the "Coating Window Suite 2010" software was established to give insight into the coating stability limitations at higher coating velocities. An analysis of PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)] in a water/isopropyl alcohol mixture as well as P3HT:PCBM [poly(3-hexylthiophene-2,5-diyl):Phenyl-C61-butyric acid methyl ester] in chlorobenzene, o-xylene and tetrahydronaphthalene showed the possibility of coating speeds up to 60 m/min. The simulation further revealed the maximum coating head distances for a given wet film thickness. Finally, we show a solar-cell with slot-die coated PEDOT:PSS and P3HT:PCBM-layer based on the parameters obtained by the simulated data, which exhibits reasonable performance. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: OPV solar cell; Slot-die coating; Coating speed

Determining the internal quantum efficiency of organic Bulk Heterojunctions based on mono and bisadduct fullerenes as acceptor - Azimi, Hamed; Morana, Mauro; Ameri, Tayebeh; Dastmalchi, Babak; Scharber, Markus; Hingerl, Kurt; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2011)
With the aid of optical modeling, the internal quantum efficiencies of organic Bulk Heterojunction (oBHJ) photovoltaic devices based on low band gap polymer of poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d] silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5, 5′-diyl] (Si-PCPDTBT) blended with the acceptors of 1-(3-Methoxycarbonyl) propyl-1-phenyl [6,6] C61 (PCBM) and bisadduct (bisPCBM) are determined. The Si-PCPDTBT:bisPCBM devices show considerably lower short circuit current density (J) as compared to the Si-PCPDTBT:PCBM devices. The results show that 30% of this smaller J is due to the lower optical absorption of bisPCBM, while the major losses originate from the electrical losses. It is found that for the best Si-PCPDTBT:bisPCBM devices with an active layer thickness in the range of 70100 nm, the inefficient charge generation within the bisPCBM domains is the major contribution to the whole losses. Increasing the active layer thickness of Si-PCPDTBT:bisPCBM device significantly enhances recombination losses in polymer/bisfullerene matrix. © 2011 Elsevier B.V. All rights reserved.
Keywords: Charge generation; Fullerene bisadduct; Internal quantum efficiency; Organic solar cell; Recombination

Development of a KOH defect etching furnace with absolute in-situ temperature measurement capability - Sakwe, Aloysius; Herro, Ziad Georges; Wellmann, Peter (Materials Science Forum, 2005)
Etching temperature and time are important parameters in the etching of SiC single crystals in molten KOH for defect studies. However, comparison of results of different research groups is difficult because of the way temperature measurements are being carried out. Until now the temperature of the melt has been measured indirectly with a temperature sensor placed outside the melt on the outer walls of the crucible of the etching furnace, resulting in varying etching conditions for varying setup designs. In this paper we developed an etching furnace with the capability of measuring the absolute temperature in-situ directly in the KOH melt. A new thermoelement, resistant to hot molten KOH was developed. Temperature profile measurements of the molten KOH were carried out and a calibration curve of the furnace was obtained. Based on our temperature measurements, we found that etching at 530 ° C for 5 minutes was optimal for defect characterisation, both for defect statistics and for distinguishing between the etch pit morphologies. At 550 ° C the etch pits become too large, overlap each other and the etching is no longer defect selectiv
Keywords: Molten KOH; etching; etching furnace; dislocations; thermoelement; temperature profile; 6H-SiC single crystals

Development of efficient and stable inverted bulk heterojunction (BHJ) solar cells using different metal oxide interfaces - Litzov, Ivan; Brabec, Christoph (Materials, 2013)
Solution-processed inverted bulk heterojunction (BHJ) solar cells have gained much more attention during the last decade, because of their significantly better environmental stability compared to the normal architecture BHJ solar cells. Transparent metal oxides (MeO) play an important role as the dominant class for solution-processed interface materials in this development, due to their excellent optical transparency, their relatively high electrical conductivity and their tunable work function. This article reviews the advantages and disadvantages of the most common synthesis methods used for the wet chemical preparation of the most relevant n-type- and p-type-like MeO interface materials consisting of binary compounds AB. Their performance for applications as electron transport/extraction layers (ETL/EEL) and as hole transport/extraction layers (HTL/HEL) in inverted BHJ solar cells will be reviewed and discussed. © copy 2013 by the authors; licensee MDPI, Basel, Switzerland.
Keywords: Device stability; Inverted structure; Metal oxide interfaces; Sol-gel methods

Device modeling of perovskite solar cells: insights and outlooks - Le Corre, Vincent Marc; Wang, Zishuai; Koster, L Jan Anton; Tress, Wolfgang (Soft-Matter Thin Film Solar Cells: Physical Processes and Device Simulation, 2020)

Device Performance of Emerging Photovoltaic Materials (Version 1) - Almora, Osbel; Baran, Derya; Bazan, Guillermo C.; Berger, Christian; Cabrera, Carlos I.; Catchpole, Kylie R.; Erten-Ela, Sule; Guo, Fei; Hauch, Jens; Ho-Baillie, Anita W.Y.; Jacobsson, T. Jesper; Janssen, Rene A.J.; et al. (Advanced Energy Materials, 2020)
Emerging photovoltaics (PVs) focus on a variety of applications complementing large scale electricity generation. Organic, dye-sensitized, and some perovskite solar cells are considered in building integration, greenhouses, wearable, and indoor applications, thereby motivating research on flexible, transparent, semitransparent, and multi-junction PVs. Nevertheless, it can be very time consuming to find or develop an up-to-date overview of the state-of-the-art performance for these systems and applications. Two important resources for recording research cells efficiencies are the National Renewable Energy Laboratory chart and the efficiency tables compiled biannually by Martin Green and colleagues. Both publications provide an effective coverage over the established technologies, bridging research and industry. An alternative approach is proposed here summarizing the best reports in the diverse research subjects for emerging PVs. Best performance parameters are provided as a function of the photovoltaic bandgap energy for each technology and application, and are put into perspective using, e.g., the Shockley–Queisser limit. In all cases, the reported data correspond to published and/or properly described certified results, with enough details provided for prospective data reproduction. Additionally, the stability test energy yield is included as an analysis parameter among state-of-the-art emerging PVs.
CRIS-Team Scopus Importer:2020-12-11
Keywords: bandgap energy; emerging photovoltaics; flexible photovoltaics; photovoltaic device photostability; transparent and semitransparent solar cells

Device Performance of Emerging Photovoltaic Materials (Version 3) - Almora, Osbel; Baran, Derya; Bazan, Guillermo C.; Cabrera, Carlos I.; Erten-Ela, Sule; Forberich, Karen; Guo, Fei; Hauch, Jens; Ho-Baillie, Anita W. Y.; Jesper Jacobsson, T.; Janssen, Rene A. J.; Kirchartz, Thomas; et al. (Advanced Energy Materials, 2023)
Following the 2nd release of the “Emerging PV reports,” the best achievements in the performance of emerging photovoltaic devices in diverse emerging photovoltaic research subjects are summarized, as reported in peer-reviewed articles in academic journals since August 2021. Updated graphs, tables, and analyses are provided with several performance parameters, e.g., power conversion efficiency, open-circuit voltage, short-circuit current density, fill factor, light utilization efficiency, and stability test energy yield. These parameters are presented as a function of the photovoltaic bandgap energy and the average visible transmittance for each technology and application, and are put into perspective using, e.g., the detailed balance efficiency limit. The 3rd installment of the “Emerging PV reports” extends the scope toward triple junction solar cells.
CRIS-Team Scopus Importer:2023-01-13
Keywords: bandgap energy; emerging photovoltaics; flexible photovoltaics; photovoltaic device operational stability; semitransparent solar cells; tandem solar cells; transparent solar cells

Device Physics of Hybrid Perovskite Solar Cells: Theory and Experiment - López-Varo, Pilar; Jiménez-Tejada, Juan A.; García-Rosell, Manuel; Garcia-Belmonte, Germà; Bisquert, Juan; Almora Rodriguez, Osbel (Advanced Energy Materials, 2018)
Perovskite solar cells exhibit a series of distinctive features in their optoelectronic response that have a decisive influence on the performance, especially for long-time response. Here is a survey of recent advances both in device simulation and optoelectronic and photovoltaic responses are provided, with the aim of covering comprehensively recent advances. Device simulations are included with clarifying discussions about the implications of classical drift-diffusion modeling and the inclusion of ionic charged layers near the outer carrier selective contacts. The outcomes of several transient techniques are summarized, along with the discussion of impedance and capacitive responses. In relation to the capacitive response, it is also a discussion on the hysteresis curve. Although alternative models and explanations are included in our discussion, the review relies upon a key mechanism. 20%, outer interfaces play a role in the performance of the PSCs. The ionic and electronic kinetics in the vicinity of the interfaces, coupled to surface recombination and carrier extraction mechanisms, should be carefully explore
Keywords: perovskite solar cell impedance spectroscopy

Differential calorimetry study of the initial stage of the sulphurisation process of CuInSe2 solar cell materials - Tang, K.; Künecke, Ulrike; Oehlschläger, Felix; Hölzing, Astrid; Schurr, R.; Hock, Rainer; Wellmann, Peter (Solar Energy Materials and Solar Cells, 2010)
Sulphurisation of CuInSe2 solar cell absorber materials is of particular interest for band gap engineering by means of compositional grading. We studied the chalcopyrite formation process of Cu-In-S-Se stacks with varying Se to S ratio from 100% Se (0% S) down to 0% Se (100% 5). Differential calorimetry (DSC) was applied as a fundamental characterization tool to track the crystal phase formation process. To verify the evolution of various crystallographic phases, DSC measurements were supplemented by temperature dependent in-situ X-ray diffraction (XRD) experiments of equivalent thin film compositions. For a S content of 25% the system is governed by sulphurisation of Cu and In, with the ternary phase CuIn5(S,Se)(8) and the binary phase Cu-2(S,Se) playing major roles in the chalcopyrite formation process. It is found that the chalcopyrite formation moves to higher temperatures if the S content is increased. (C) 2010 Elsevier B.V. All rights reserved.
Keywords: CuIn(S; Se)2; Chalcopyrite; Thin films; Sequential processing; Thermal analys

Digital x-ray imaging of SiCPVT process: Analysis of crystal growth and powder source degradation - Wellmann, Peter; Bickermann, Matthias; Hofmann, Heinz-Dieter; Kadinski, Lev; Selder, Markus; Straubinger, Thomas; Winnacker, Albrecht (Materials Science Forum, 2000)
Using digital x-ray imaging during silicon carbide (SiC) physical vapor transport process the SiC crystal growth as well as SiC powder source degradation have been monitored online. Using digital image processing we have (i) extracted from the x-ray shots the shape of the crystal growth interface, (ii) determined the crystal growth rate and (iii) analyzed the evolution of the SiC source material by determining its density as a function of progressing process time. The underlying sublimation and crystallization effects are discusse
Keywords: PVT Process; SiC Powder; X-Ray Imaging

Dimensional Regulation of Organic n-Type Dopants for Highly Efficient Perovskite Solar Cells and Modules - Liu, Cong; Zuo, Chen; Xue, Qifan; Lin, Dongxu; Liu, Tao; Luo, Jun; Huang, Hao; Chen, Kai; Gao, Yanyan; Zeng, Jie; Zhang, Yong; Xu, Baomin; et al. (Advanced Materials, 2025)
A strong n-type perovskite layer is crucial in achieving high open-circuit voltage (VOC) and power conversion efficiency (PCE) in the p-i-n solar cells, as the weak n-type perovskites result in a loss of VOC, and the p-type perovskites contain numerous electron traps that cause the severe carrier recombination. Here, three types of perylene diimide (PDI) based small molecule dopants with different dimensions, including 1D-PDI, 2D-PDI, and 3D-PDI are designed, to produce heavier n-type perovskites. The PDI-based molecules with Selenium atoms have a strong electron-donating ability, effectively enlarging the quasi-Fermi level splitting within the perovskites. Besides, the PDI molecules can coat the surface of the perovskite crystal to form the lattice cage through their conjugate skeletons, which passivates the trap states and improves the n-doping efficiency, as well as the stabilities of perovskites and related devices. With the addition of the 2D-PDI, the small-area solar cells achieved a PCE of 26.06% (25.44% certified) with a high VOC of 1.18 V and a remarkable fill factor of 87.23%. Furthermore, the rigid and flexible perovskite solar modules yielded high PCEs of 21.48% and 20.71%, respectively. This dimensional regulation strategy provides useful guidance for effective n-type doping and high-performance p-i-n solar cells.
CRIS-Team Scopus Importer:2025-02-07
Keywords: conversion efficiency; dimensional regulation; lattice cage; n-type doping; perovskite solar cells

Direct Observation of Stable Negative Capacitance in SrTiO3@BaTiO3 Heterostructure - Wang, Zhongyang; Li, Hongyu; Hu, Huiying; Fan, Yuqi; Fan, Runhua; Li, Baowen; Zhang, Jiaoxia; Liu, Hu; Fan, Jincheng; Hou, Hua; Dang, Feng; Kou, Zongkui; et al. (Advanced Electronic Materials, 2019)
Negative capacitance in ferroelectrics has seem remarkable progress in recent years. However, direct measurement of negative capacitance has so far been a challenge due to its instable characteristic in the electrostatic field. An ingenious method to design stable negative capacitance by dielectric resonance under high-frequency alternating electric fields is demonstrated. The well-pronounced dielectric resonance and electrical property in BaTiO3/SrTiO3 (BT/ST) bulk ceramics consisted of epitaxial core-shell particles are studied. As the negative capacitance can be considered as an inductive behavior, the dielectric resonance of permittivity induced by a LC resonance can be occurred. The dielectric resonance can be described by the Lorentz model and explained by Fano-like resonance of TO2 phonon in BT. In addition, lowest resonant frequency is observed at effective Curie temperature. Benefiting from negative capacitance in the BT/ST ceramics, both high permittivity and negative permittivity are accompanied with low losses around the resonant frequency, which is useful for developing capacitors and metamaterials. Significantly, this work will provide an initiative avenue to obtain explicit negative capacitance of ferroelectrics in the frequency spectrum.
CRIS-Team WoS Importer:2019-12-27

Direct observation of surface polarization at hybrid perovskite/Au interfaces by dark transient experiments - Caram, Jorge; Garcia-Batlle, Marise; Almora, Osbel; Arce, Roberto D.; Guerrero, Antonio; Garcia-Belmonte, Germa (Applied Physics Letters, 2020)
A distinctive feature of hybrid perovskite light-absorbing materials is the non-negligible ionic conductivity influencing photovoltaic performance and stability. Moving ions or vacancies can naturally accumulate at the outer interfaces (electrode polarization) upon biasing. Contrary to that approach, a modulation of conductive or recombination properties could manifest as an alteration in the low-frequency part of the impedance response, either producing inductive or large capacitive features. Under this last view, capacitances are not the response of polarized structures or charging mechanisms, but result from the modulation of currents. This work intends to provide pieces of evidence that assist us in distinguishing between these two dissimilar mechanisms, namely, real charge polarization and delayed current effects under bias in the dark. The analysis relays upon an experimental technique based on transient charging signals using the Sawyer-Tower circuit. Instead of applying an alternating small perturbation over a steady-state voltage (differential capacitance method), transient charging measures the resulting polarization upon a large bias step under the suppression of dc currents. Our findings reveal that real steady-state charge is indeed induced by the applied voltage in the dark, easily interpreted by means of charged real capacitors with values much larger than the geometrical capacitance of the film. The connection between that polarization and the charging of perovskite/contact interfaces is highlighted.
CRIS-Team WoS Importer:2020-05-29

Discerning recombination mechanisms and ideality factors through impedance analysis of high-efficiency perovskite solar cells - Almora, Osbel; Cho, Kyung Taek; Aghazada, Sadig; Zimmermann, Iwan; Matt, Gebhard; Brabec, Christoph; Nazeeruddin, Mohammad Khaja; Garcia-Belmonte, Germa (Nano Energy, 2018)
The ubiquitous hysteresis in the current-voltage characteristic of perovskite solar cells (PSCs) interferes in a proper determination of the diode ideality factor (n), a key parameter commonly adopted to analyze recombination mechanisms. An alternative way of determining n is by measuring the voltage variation of the ac resistances in conditions of negligible steady-state dc currents. A reliable analysis of n based on the determination of the resistive response, free of hysteretic influences, reveals two separated voltage exponential dependences using different perovskite absorbers (3D perovskites layer based on CH3NH3PbI3 or mixed Cs(0.1)FA(0.74)MA(0.13)PbI(2.48)Br(0.39)) and a variety of interlayers (2D perovskite thin capping). The dominant resistive element always exhibits an exponential dependence with factor n approximate to 2, irrespective of the type of perovskite and capping layers. In addition, a non-negligible resistive mechanism occurs at low-frequencies (with voltage-independent time constant similar to 1 s) which is related to the kinetic properties of the outer interfaces, with varying ideality factor (n = 2 for CH3NH3PbI3, and n = 1.5 for Cs(0.1)FA(0.74)MA(0.13)PbI(2.48)Br(0.39)). Our work identifies common features in the carrier recombination mechanisms among different types of high-efficiency PSCs, and simultaneously signals particularities on specific architectures, mostly in the carrier dynamics at outer interfaces.
Keywords: Perovskites solar cells; Recombination; Impedance spectroscopy; Capacitance; 2D capping

Discovering hidden relations in organic semiconductor composites – a concept to accelerate the development of organic photovoltaics - Brabec, Christoph (13th Conference on Hybrid and Organic Photovoltaics (HOPV21), 2021)
While c-Si appears untouchable as leading PV main stream technology for a longer time, many of the new applications which rely on flexibility, transparency, colour management, integrability or simply elegant appearance require novel photovoltaic materials and technologies. Organic photovoltaics (OPV), like other emerging thin film PV technologies, are not yet part of this global TW scenario. The first printed PV products were launched in 2008/2009 for portable chargers at an efficiency of about 2 %. Despite the rather low performance at that time, these first products already showed the characteristic “OPV features” like flexibility, transparency and colour variability. Since then, the printed PV community has concentrated on developing novel material systems for higher efficiency – a development which was outstandingly successful. In the last 10 years. Organic solar modules with close to 13 % efficiency were certified in 2020, while single junction cells already reach 18 % power conversion efficiency. Despite the great process, OPV is still facing multiple challenges, from lifetime to cost and to environmental aspects. The most urgent question therefore is – how can we accelerate the development of organic solar cells towards a market ready product. In this talk I will discuss concepts and strategies to speed-up the development of OPV technologies towards an earlier deployment on the market. Automated, robot-based research lines with shared interfaces to multi-objective machine learning based optimization routines are introduced as a powerful concept to accelerate the development of new materials towards markets. Despite the commonly accepted understanding that machine learning algorithms can accelerate optimization, we demonstrate that physical model-based AI is superior in discovering hidden relations. We will demonstrate that in specific cases it is becoming possible to predict efficiency or even stability of organic solar cells based on a simple absorption measurement.

Discovery of temperature-induced stability reversal in perovskites using high-throughput robotic learning - Zhao, Yicheng; Hauch, Jens; Zhang, Jiyun; Xu, Zhengwei; Sun, Shijing; Langner, Stefan; Hartono, Noor Titan Putri; Heumüller, Thomas; Hou, Yi; Elia, Jack; Li, Ning; Matt, Gebhard; et al. (Nature Communications, 2021)
Stability of perovskite-based photovoltaics remains a topic requiring further attention. Cation engineering influences perovskite stability, with the present-day understanding of the impact of cations based on accelerated ageing tests at higher-than-operating temperatures (e.g. 140°C). By coupling high-throughput experimentation with machine learning, we discover a weak correlation between high/low-temperature stability with a stability-reversal behavior. At high ageing temperatures, increasing organic cation (e.g. methylammonium) or decreasing inorganic cation (e.g. cesium) in multi-cation perovskites has detrimental impact on photo/thermal-stability; but below 100°C, the impact is reversed. The underlying mechanism is revealed by calculating the kinetic activation energy in perovskite decomposition. We further identify that incorporating at least 10 mol.% MA and up to 5 mol.% Cs/Rb to maximize the device stability at device-operating temperature (<100°C). We close by demonstrating the methylammonium-containing perovskite solar cells showing negligible efficiency loss compared to its initial efficiency after 1800 hours of working under illumination at 30°C.
CRIS-Team Scopus Importer:2021-05-21

Discriminating bulk versus interface shunts in organic solar cells by advanced imaging techniques - Karl, André; Osvet, Andres; Vetter, Andreas; Maisch, Philipp; Li, Ning; Egelhaaf, Hans Joachim; Brabec, Christoph (Progress in Photovoltaics: Research and Applications, 2019)
An important aspect when upscaling organic photovoltaics from laboratory to industrial scale is quality control. Established imaging techniques like lock‐in thermography or luminescence imaging are frequently used for this purpose. While these techniques allow for the lateral detection of defects, they cannot provide information on the vertical position of the defect in the OPV stack. Here, we present an approach to overcome this limitation. A femtosecond‐laser is deployed to introduce well‐defined artificial calibration defects selectively into both the interface and the bulk active layer of inverted P3HT:PCBM bulk heterojunction cells during device fabrication. The defective cells are then characterized using J‐V analysis and several nondestructive imaging methods (dark lock‐in thermography, photoluminescence, and electroluminescence imaging). The distinct response for each defect in the different imaging methods enables us to uniquely distinguish between bulk and interface defects. This allows to study surface recombination under most controlled conditions.
Keywords: imaging; organic solar cells; dark lock-in thermography; electroluminescence; photoluminescence; quality control

Dislocation arrangements in 4H-SiC and their influence on the local crystal lattice properties - Roder, Melissa; Steiner, Johannes; Wellmann, Peter; Kabukcuoglu, Merve; Hamann, Elias; Haaga, Simon; Hänschke, Daniel; Danilewsky, Andreas (Journal of Applied Crystallography, 2023)
Two wafers of one 4H-silicon carbide (4H-SiC) bulk crystal, one cut from a longitudinal position close to the crystal’s seed and the other close to the cap, were characterized with synchrotron white-beam X-ray topography (SWXRT) in back-reflection and transmission geometry to investigate the dislocation formation and propagation during growth. For the first time, full wafer mappings were recorded in 00012 back-reflection geometry with a CCD camera system, providing an overview of the dislocation arrangement in terms of dislocation type, density and homogeneous distribution. Furthermore, by having similar resolution to conventional SWXRT photographic film, the method enables identification of individual dislocations, even single threading screw dislocations, which appear as white spots with a diameter in the range of 10 to 30 mm. Both investigated wafers showed a similar dislocation arrangement, suggesting a constant propagation of dislocations during crystal growth. A systematic investigation of crystal lattice strain and tilt at selected wafer areas with different dislocation arrangements was achieved with high-resolution X-ray diffractometry reciprocal-space map (RSM) measurements in the symmetric 0004 reflection. It was shown that the diffracted intensity distribution of the RSM for different dislocation arrangements depends on the locally predominant dislocation type and density. Moreover, the orientation of specific dislocation types along the RSM scanning direction has a strong influence on the local crystal lattice properties.
CRIS-Team Scopus Importer:2024-12-16
Keywords: 4H-SiC; crystal growth; dislocations; high-resolution X-ray diffractometry; reciprocal-space maps; synchrotron white-beam X-ray topography

Dislocation evolution and distribution during physical vapor transport (PVT) growth of bulk 6H-SiC single crystals - Sakwe, Aloysius; Müller, Ralf; Masri, P.; Wellmann, Peter (Physica Status Solidi C: Conferences, 2006)
In this paper we report in a systematic way on the evolution and distribution of dislocations in PVT 6H-SiC single crystals grown under different conditions. Using KOH defect etching and optical microscopy, we have performed dislocation tracking along the crystal lengths to study their evolution and propagation mechanisms based on statistics. In particular, crystal growth experiments with continuously increased temperature during the process time have been performed to investigate the role of temperature on dislocation formation and on their annihilation behavior. We discuss dislocation evolution and distribution in this particular PVT growth process as compared to those with a constant process temperature. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Keywords: SiC; 6H SiC; dislocations; PVT; KOH etching

Disorder-Induced Open-Circuit Voltage Losses in Organic Solar Cells during Photoinduced Burn-In - Heumueller, Thomas; Burke, Timothy M.; Mateker, William R.; Sachs-Quintana, Isaac T.; Vandewal, Koen; Brabec, Christoph; Mcgehee, Michael D. (Advanced Energy Materials, 2015)
The photoinduced open-circuit voltage (Voc) loss commonly observed in bulk heterojunction organic solar cells made from amorphous polymers is investigated. It is observed that the total charge carrier density and, importantly, the recombination dynamics are unchanged by photoinduced burn-in. Charge extraction is used to monitor changes in the density of states (DOS) during degradation of the solar cells, and a broadening over time is observed. It is proposed that the Voc losses observed during burn-in are caused by a redistribution of charge carriers in a broader DOS. The temperature and light intensity dependence of the Voc losses can be described with an analytical model that contains the amount of disorder broadening in a Gaussian DOS as the only fit parameter. Finally, the Voc loss in solar cells made from amorphous and crystalline polymers is compared and an increased stability observed in crystalline polymer solar cells is investigated. It is found that solar cells made from crystalline materials have a considerably higher charge carrier density than those with amorphous materials. The effects of a DOS broadening upon aging are suppressed in solar cells with crystalline materials due to their higher carrier density, making crystalline materials more stable against Voc losses during burn-in.
Keywords: charge carrier densities; disorders; morphology; organic photovoltaics; solar cells; stabilities

Do Capacitance Measurements Reveal Light-Induced Bulk Dielectric Changes in Photovoltaic Perovskites? - Almora Rodriguez, Osbel; Aranda, Clara; Garcia-Belmonte, Germà (Journal of Physical Chemistry C, 2018)
Several studies have identified complex interactions between photogenerated carriers and the crystal lattice in perovskite materials for photovoltaics, which are considered to have an inherently soft character. Light is known to induce phase segregation in mixed halide perovskites, enhance piezoelectricity, and change dipole moments of the unit cell. Therefore, it is considered that photogenic variations in bulk polarizability and dielectric properties. Light-induced bulk polarization changes should be observable by capacitance measurements, preferably at intermediate frequencies where the geometric capacitance dominates. However, capacitance spectra are influenced by several capacitive and resistive mechanisms, which are thus modulated by light. Capacitances may arise from dielectric bulk polarization, space-charge depletion zones, chemical electronic bulk storage, and interfacial accumulation mechanisms. This variety of capacitive mechanisms may induce wrong interpretation and produce misleading outcomes when uncritically connected to the bulk polarization response. The actual value of the geometric capacitance is shown in the figure below. Careful analyzes are then needed before attributing the light-induced modulation of the measured capacitance to hybrid perovskite dielectric changes. The actual value of the geometric capacitance is shown in the figure below. Careful analyzes are then needed before attributing the light-induced modulation of the measured capacitance to hybrid perovskite dielectric changes. The actual value of the geometric capacitance is shown in the figure below. Careful analyzes are then needed before attributing the light-induced modulation of the measured capacitance to hybrid perovskite dielectric changes.<br

Does Covid-19 Impact Photovoltaics? - Peters, Ian Marius; Brabec, Christoph; Buonassisi, Tonio; Hauch, Jens; Nobre, Andre M. (2020 47TH IEEE PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC), 2020)
CRIS-Team WoS Importer:2021-06-25

Dopant-Free Bithiophene-Imide-Based Polymeric Hole-Transporting Materials for Efficient and Stable Perovskite Solar Cells - Bai, Yuanqing; Zhou, Zhisheng; Xue, Qifan; Liu, Chunchen; Li, Ning; Tang, Haoran; Zhang, Jiabin; Xia, Xinxin; Zhang, Jie; Lu, Xinhui; Brabec, Christoph; Huang, Fei (Advanced Materials, 2022)
The development of hole-transport materials (HTMs) with high mobility, long-term stability, and comprehensive passivation is significant for simultaneously improving the efficiency and stability of perovskite solar cells (PVSCs). Herein, two donor-acceptor (D-A) conjugated polymers PBTI and PFBTI with alternating benzodithiophene (BDT) and bithiophene imide (BTI) units are successfully developed with desirable hole mobilities due to the good planarity and extended conjugation of molecular backbone. Both copolymers can be employed as HTMs with suitable energy levels and efficient defect passivation. Shortening the alkyl chain of the BTI unit and introducing fluorine atoms on the BDT moiety effectively enhances hole mobility and hydrophobicity of the HTMs, leading to improved efficiency and stability of PVSCs. As a result, the organic-inorganic hybrid PVSCs with PFBTI as the HTM deliver a power conversion efficiency (PCE) of 23.1% with enhanced long-term operational and ambient stability, which is one of the best efficiencies reported for PVSCs with dopant-free polymeric HTMs to date. Moreover, PFBTI can be applied in inorganic PVSCs and perovskite/organic tandem solar cells, achieving a high PCE of 17.4% and 22.2%, respectively. These results illustrate the great potential of PFBTI as an efficient and widely applicable HTM for cost-effective and stable PVSCs.
CRIS-Team WoS Importer:2022-11-11

Dopant-Free Hole-Transporting Material with Enhanced Intermolecular Interaction for Efficient and Stable n-i-p Perovskite Solar Cells - Wang, Jing; Wu, Xin; Liu, Yizhe; Qin, Tian; Zhang, Kaicheng; Li, Ning; Zhao, Juan; Ye, Ruquan; Fan, Zhanxi; Chi, Zhenguo; Zhu, Zonglong (Advanced Energy Materials, 2021)
Developing low-cost, efficient, and stable dopant-free hole-transporting materials (HTMs) in perovskite solar cells (PVSCs) is essential to their commercial deployment. Herein, the synthesis of a novel spirofluorene-dithiolane based small molecular HTM, SFDT-TDM, through facile and low-cost synthetic routes is reported. The C-H…π interactions in adjacent SFDT-TDM are beneficial for high hole mobility and the methylthio groups in SFDT-TDM can serve as Lewis bases to passivate the defects on the surface of perovskite films, leading to suppressed non-radiative recombination and enhanced charge extraction at the perovskite/HTM interface. As a result, CsxFA1−xPbI3 based PVSCs with SFDT-TDM as the HTM realize champion power conversion efficiencies (PCEs) of 21.7% and 20.3% for small-area (0.04 cm2) and large-area (1.0 cm2) devices with negligible photocurrent hysteresis, respectively. Additionally, all-inorganic CsPbI3−xBrx based PVSCs with SFDT-TDM demonstrate an impressive PCE of 17.1% along with excellent stability. This work highlights the great potential of the spirofluorene core for exploring low-cost and dopant-free HTMs for PVSCs with high efficiency and stability.
CRIS-Team Scopus Importer:2021-07-02
Keywords: defect passivation; dopant-free HTM; inorganic perovskites; MA-free perovskites; perovskite solar cells

Dopant mapping in highly p-doped silicon by micro-Raman spectroscopy at various injection levels - Kunz, Thomas; Hessmann, Maik T.; Seren, S.; Meidel, B.; Terheiden, B.; Brabec, Christoph (Journal of Applied Physics, 2013)
Micro-Raman spectroscopy has been used to investigate the acceptor distribution in highly p-doped silicon. As an example, the dopant distribution in crystalline thin-film layers, as developed for solar cells, was mapped. The method is based on the analysis of the Fano-type Raman peak shape which is caused by free charge carriers. For calibration of the Raman acceptor measurements (excitation at a wavelength of 532 nm), we used mono-crystalline reference samples whose acceptor concentration was determined by electrochemical capacitance voltage. We find a significant influence of light induced free charge carriers on the peak shape which results from typical Raman excitation. Thus, the selection of a suitable intensity is important to avoid a too low signal-to-noise ratio on the one hand and systematic errors due to light induced carriers on the other hand. Different evaluation methods, i.e., peak asymmetry versus peak width analysis, are compared in respect to interference caused by random noise of the spectra or else by internal stress in the sample. While the width analysis method is more robust to a low signal-to-noise ratio, the symmetry analysis is more reliable in case of high intrinsic stress. © 2013 American Institute of Physics.
Keywords: Acceptor concentrations; Analysis method; Dopant distribution; Electrochemical capacitance voltage; Evaluation methods; Free charge carriers; Injection levels; Intrinsic stress; Low signal-to-noise ratio; Micro Raman Spectroscopy; Peak asymmetry; Peak shapes; Peak widths; Raman excitation; Raman peak; Random noise; Symmetry analysis; Thin film layers Engineering controlled terms: Charge carriers; Crystalline materials; Phosphorus; Raman spectroscopy; Signal to noise ratio Engineering main heading: Silicon

Doping/Alloying Pathways to Lead-Free Halide Perovskites with Ultimate Photoluminescence Quantum Yields - Stroyuk, Oleksandr; Raievska, Oleksandra; Hauch, Jens; Brabec, Christoph (Angewandte Chemie International Edition, 2022)
Tailored modifications of halide lead-free perovskites (LFPs) via doping/alloying with metal cations have been recognized as a promising pathway to highly efficient inorganic phosphors with photoluminescence (PL) quantum yields of up to 100%. Such materials typically reveal selective sensitivity to UV light, a broad PL range, large PL lifetimes as well as a unique compositional variability and stability – an ideal combination for many light-harvesting applications. The minireview presents the state-of-the-art in doped LFPs, focusing on the reports published mostly in the last 2-3 years. We discuss the factors determining the efficiency and spectral parameters of the broadband PL of doped LFPs depending on the dopant and host matrix, both in micro- and nanocrystalline states, address the most relevant challenges this rapidly developing research area is facing, and outline the most promising concepts to further progress in this field to be achieved.
CRIS-Team Scopus Importer:2022-12-16
Keywords: elpasolites; inorganic perovskites; light conversion; light emission; photophysical properties

Doping of Mesoscopic Charge Extraction Layers Enables the Design of Long-Time Stable Organic Solar Cells - Xu, Junyi; Luo, Junsheng; Gubanov, Kirill; Barabash, Anastasia; Fink, Rainer; Heumüller, Thomas; Brabec, Christoph (ACS Energy Letters, 2024)
Realizing efficient and stable organic solar cells (OSCs) via all-solution processing requires the design of tailored charge extraction interfaces. Herein, we demonstrate a substantially different interface concept for OSC that is based on a low-temperature processed mesoscopic hole transporting layer (HTL) derived from partially covered organic nanoparticles (NPs) in the n-i-p structure. The mesoscopic interface is further doped in a second coating step with an organic salt dopant, BCF-Li. The interactions among the dopant, the solvent for sequential doping, and the semiconductor layer are surprisingly complex. The mesoscopic interface is necessary to evenly wet the semiconductor and prevent the aggregation of the dopant. At the same time, the sequential process reduces the excess acceptor at the interface. Both processes together are necessary to generate an efficiently doped interface for low-Ohmic-charge extraction and stable contacts. Devices with fully solution-processed mesoscopic interfaces show a superb shelf lifetime of over 22000 h without encapsulation and a long-term operational stability under 1 sun illumination for 2000 h (T80). Flexible devices bypass 1000 bending cycles with negligible degradation. Mesoscopic doped interfaces are demonstrated as an alternative to PEDOT:PSS as well as PEDOT related interface concepts for nonfullerene acceptors (NFA) in the n-i-p architecture.
CRIS-Team Scopus Importer:2024-01-12

Double-Cable Conjugated Polymers Based on Simple Non-Fused Electron Acceptors for Single-Component Organic Solar Cells - Liu, Baiqiao; Liang, Shijie; Karuthedath, Safakath; He, Yakun; Wang, Jing; Tan, Wen Liang; Li, Hao; Xu, Yunhua; Laquai, Frederic; Brabec, Christoph; Mcneill, Christopher R.; Xiao, Chengyi; et al. (Macromolecules, 2023)
In this work, a non-fused electron acceptor with near-infrared absorption was introduced into double-cable conjugated polymers for single-component organic solar cells (SCOSCs). The non-fused electron acceptor contains a simple thienyl-phenyl-thienyl core with 2-(3-oxo-2,3-dihydroinden-1ylidene)malononitrile (IC) as the end group, which was used as the side unit to create double-cable conjugated polymers. In addition, poly(benzodithiophene) was selected as the conjugated backbone, in which the number of chlorine (Cl) atoms was varied to tune the optical and electronic properties. The new double-cable polymers were successfully applied in SCOSCs, providing an efficiency of over 8% with a broad photoresponse from 300 to 800 nm. When the number of Cl atoms on the repeat unit was increased from 2 to 3, the open-circuit voltage was enhanced to 1.01 V, yielding a low voltage loss of 0.59 eV, while the efficiency was reduced to 5.28%. The reduced performance is explained by the increased charge recombination in this polymer, as observed by transient absorption spectroscopy. This work reports a set of IC-based NIR double-cable conjugated polymers, which inspire material design toward more efficient SCOSCs.
CRIS-Team WoS Importer:2023-02-24

Double-Cable Conjugated Polymers with Pendent Near-Infrared Electron Acceptors for Single-Component Organic Solar Cells - Liang, Shijie; Liu, Baiqiao; Karuthedath, Safakath; Wang, Jing; He, Yakun; Tan, Wen Liang; Li, Hao; Xu, Yunhua; Li, Ning; Hou, Jianhui; Tang, Zheng; Laquai, Frederic; et al. (Angewandte Chemie International Edition, 2022)
Double-cable conjugated polymers with near-infrared (NIR) electron acceptors are synthesized for use in single-component organic solar cells (SCOSCs). Through the development of a judicious synthetic pathway, the highly sensitive nature of the 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC)-based electron acceptors in basic and protonic solvents is overcome. In addition, an asymmetric design motif is adopted to optimize the packing of donor and acceptor segments, enhancing charge separation efficiency. As such, the new double-cable polymers are successfully applied in SCOSCs, providing an efficiency of over 10 % with a broad photo response from 300 to 850 nm and exhibiting excellent thermal/light stability. These results demonstrate the powerful design of NIR-acceptor-based double-cable polymers and will enable SCOSCs to enter a new stage.
CRIS-Team WoS Importer:2022-07-29

Double-Side-Passivated Perovskite Solar Cells with Ultra-low Potential Loss - Zhao, Yicheng; Li, Qi; Zhou, Wenke; Hou, Yi; Zhao, Yao; Fu, Rui; Yu, Dapeng; Liu, Xin; Zhao, Qing (Solar RRL, 2019)
An ideal crystal quality in the grain interior of perovskite polycrystalline films is well recognized; therefore, understanding interfacial impact and the ways to limit interfacial recombination is critical to fabricating highly efficient solar cells. In perovskite solar cells, PbI2 has been used to passivate defects at grain boundaries, yet a systematic PbI2 passivation engineering to boost the high-performance perovskite solar cells has not been fully explored. Here, a novel device structure comprised of double-side-passivated perovskite solar cells (DSPC) is devised through intentionally distributing PbI2 to both the front/rear-side surfaces and grain boundaries of the formamidinium-lead-iodide-based (FAPbI(3)-based) perovskite film. The minority carrier lifetime in double-side-passivated perovskite is extended to 1.1s with single-exponential decay using time-resolved photoluminescence. This result indicates a generic passivation effect of PbI2 on perovskite interfaces, resembling SiO2 passivation in silicon solar cells. Correspondingly, the best photovoltaic device with TiO2-based planar structure presents a stabilized efficiency of 22%. Moreover, DSPC effectively boosts the limits of open circuit voltages toward a record potential loss of 0.38V for 1.53eV-bandgap perovskites. The architecture of double-side-passivated perovskite opens up new opportunities to exceed the efficiency of state-of-the-art perovskite solar cells.
CRIS-Team WoS Importer:2019-03-08

Dual functionality of charge extraction and interface passivation by self-assembled monolayers in perovskite solar cells - Azam, Muhammad; Du, Tian; Wan, Zhongquan; Zhao, Heng; Zeng, Huaibiao; Wei, Runmin; Brabec, Christoph; Luo, Junsheng; Jia, Chunyang (Energy and Environmental Science, 2024)
Perovskite solar cells (PSCs) have shown significant advancements in their device performance; however, their poor long-term stability under operational conditions is a major hurdle that hinders their commercialization. Effective bottom interfacial passivation is crucial for enhancing the device performance. Among the many approaches, self-assembled monolayers (SAMs) are particularly notable due to their exceptional ability for both charge extraction and interfacial defect passivation. In this review, we first demonstrate the issues concealed at the bottom interface and the working mechanisms for the phase separation-based fabrication of p-i-n PSCs. Subsequently, a comprehensive comparison is conducted among various SAMs, which passivate defects in the perovskite bottom interface and charge transport layers (CTLs) and modify the substrate surface properties. Furthermore, recent advancements in understanding how variations in the molecular structure of SAMs influence charge transport and their capability for defect passivation are summarized. Finally, a thought-provoking perspective is presented to stimulate the development of SAM molecules with dual functionality in terms of both carrier extraction and defect passivation.
CRIS-Team Scopus Importer:2024-10-18

Dual Interfacial Design for Efficient CsPbI2Br Perovskite Solar Cells with Improved Photostability - Tian, Jingjing; Xue, Qifan; Tang, Xiaofeng; Chen, Yuxuan; Li, Ning; Hu, Zhicheng; Shi, Tingting; Wang, Xin; Huang, Fei; Brabec, Christoph; Yip, Hin Lap; Cao, Yong (Advanced Materials, 2019)
A synergic interface design is demonstrated for photostable inorganic mixed‐halide perovskite solar cells (PVSCs) by applying an amino‐functionalized polymer (PN4N) as cathode interlayer and a dopant‐free hole‐transporting polymer poly[5,5′‐bis(2‐butyloctyl)‐(2,2′‐bithiophene)‐4,4′‐dicarboxylate‐alt‐5,5′‐2,2′‐bithiophene] (PDCBT) as anode interlayer. First, the interfacial dipole formed at the cathode interface reduces the workfunction of SnO2, while PDCBT with deeper‐lying highest occupied molecular orbital (HOMO) level provides a better energy‐level matching at the anode, leading to a significant enhancement in open‐circuit voltage (Voc) of the PVSCs. Second, the PN4N layer can also tune the surface wetting property to promote the growth of high‐quality all‐inorganic perovskite films with larger grain size and higher crystallinity. Most importantly, both theoretical and experimental results reveal that PN4N and PDCBT can interact strongly with the perovskite crystal, which effectively passivates the electronic surface trap states and suppresses the photoinduced halide segregation of CsPbI2Br films. Therefore, the optimized CsPbI2Br PVSCs exhibit reduced interfacial recombination with efficiency over 16%, which is one of the highest efficiencies reported for all‐inorganic PVSCs. A high photostability with a less than 10% efficiency drop is demonstrated for the CsPbI2Br PVSCs with dual interfacial modifications under continuous 1 sun equivalent illumination for 400 h.
CRIS-Team Scopus Importer:2019-05-02
Keywords: all-inorganic perovskite solar cells; high efficiency; interface modification; photoinduced halide segregation; surface passivation

Durable all-inorganic perovskite tandem photovoltaics - Duan, Chenghao; Zhang, Kaicheng; Peng, Zijian; Li, Shiang; Zou, Feilin; Wang, Feng; Li, Jiong; Zhang, Zheng; Chen, Chang; Zhu, Qiliang; Qiu, Jianhang; Lu, Xinhui; et al. (Nature, 2025)
All-inorganic perovskites prepared by substituting the organic cations (for example, methylammonium and formamidinium) with inorganic cations (for example, Cs+) are effective concepts to enhance the long-term photostability and thermal stability of perovskite solar cells (PSCs)1,2. Hence, inorganic perovskite tandem solar cells (IPTSCs) are promising candidates for breaking the efficiency bottleneck and addressing the stability issue, too3,4. However, challenges remain in fabricating two-terminal (2T) IPTSCs due to the inferior film formation and deep trap states induced by tin cations5-7. Here a ligand evolution (LE) strategy with p-toluenesulfonyl hydrazide (PTSH) is used to regulate film formation and eliminate deep traps in inorganic narrow-bandgap (NBG) perovskites, enabling the successful development of 2T IPTSCs. Accordingly, the 1.31 eV CsPb0.4Sn0.6I3:LE device delivers a record efficiency of 17.41%. Combined with the 1.92 eV CsPbI2Br top cell, 2T IPTSCs exhibit a champion efficiency of 22.57% (certified, 21.92%). Moreover, IPTSCs are engineered to deliver remarkable durability under maximum power point (MPP) tracking, maintaining 80% of their initial efficiency at 65 °C for 1,510 h and at 85 °C for 800 h. We elucidate that LE deliberately leverages multiple roles for inorganic NBG perovskite growth and anticipate that our study provides an insightful guideline for developing high-efficiency and stable IPTSCs.
CRIS-Team Scopus Importer:2025-02-17

Dynamics of backsheet-driven insulation issues - Buerhop-Lutz, Claudia; Lüer, Larry; Stroyuk, Oleksandr; Hauch, Jens; Peters, Ian Marius (Solar Energy Materials and Solar Cells, 2023)
To reap in the full benefit of high-efficiency solar cells and modules, the quality of the polymer encapsulant and backsheet (BS) materials is essential. Recent field studies show that early degrading backsheets cause safety issues and inverter shutdowns, resulting in yield losses. The dynamic development of degradation is important but is rarely studied because of the lack of proper datasets with meaningful and sufficient data. We studied inverter data of solar panels with a combined capacity of about 1 MWp for more than nine years including ground impedance (GI), and we labelled BS-types using our in-house identification method. Every inverter was connected to modules with exclusively a single BS-type, namely three-multilayer BSs denoted by their outer air layer: PA (polyamide), FC (fluorinated coating), and PVDF (polyvinylidene fluoride). We present, for the first time, an analysis of the degradation dynamics of GI, using a trained Gaussian Process Regression model. Using this model, we derived key degradation parameters, namely GI loss rates and time points for the onset of degradation. We found that PVDF BSs are associated with very low GI loss rates, while loss rates for PA are threefold higher with an onset at 6.6 year of operation for PA. FC BS-related loss rates were humidity dependent and two times higher those of PA; the onset was determined at 4.9 year of operation.
CRIS-Team Scopus Importer:2023-07-21
Keywords: Backsheet; Degradation rate; Gaussian Process Regression; Insulation resistance; Machine learning

Effective Ligand Engineering of the Cu2ZnSnS4 Nanocrystal Surface for Increasing Hole Transport Efficiency in Perovskite Solar Cells - Khanzada, Laraib Sarfraz; Levchuk, Ievgen; Hou, Yi; Azimi, Seyed Hamed; Osvet, Andres; Ahmad, Rameez; Brandl, Marco; Herre, Patrick; Distaso, Monica; Hock, Rainer; Peukert, Wolfgang; Batentschuk, Miroslaw; et al. (Advanced Functional Materials, 2016)
Effective engineering of surface ligands in semiconductor nanocrystals can facilitate the electronic interaction between the individual nanocrystals, making them promising for low-cost optoelectronic applications. Here, the use of high purity CuZnSnS (CZTS) nanocrystals as the photoactive layer and hole-transporting material is reported in low-temperature solution-processed solar cells. The high purity CZTS nanocrystals are prepared by engineering the surface ligands of CZTS nanocrystals, capped originally with the long-chain organic ligand oleylamine. After ligand removal, CZTS nanocrystals show substantial improvement in photoconductivity and mobility, displaying also an appreciable photoresponse in a simple heterojunction solar cell architecture. More notably, CZTS nanocrystals exhibit excellent hole-transporting properties as interface layer in perovskite solar cells, yielding power conversion efficiency (PCE) of 15.4% with excellent fill factor (FF) of 81%. These findings underscore the importance of removing undesired surface ligands in nanocrystalline optoelectronic devices, and demonstrate the great potential of CZTS nanocrystals as both active and passive material for the realization of low-cost efficient solar cells.
Keywords: CZTS solar cells; HTM; Inorganic nanocrystals; Ligand exchange; Perovskite

Effective Ligand Passivation of Cu2O Nanoparticles through Solid-State Treatment with Mercaptopropionic Acid - Azimi, Seyed Hamed; Kuhri, Susanne; Osvet, Andres; Matt, Gebhard; Khanzada, Laraib Sarfraz; Lemmer, Mario; Luechinger, Norman A.; Larsson, Mats I.; Zeira, Eitan; Guldi, Dirk Michael; Brabec, Christoph (Journal of the American Chemical Society, 2014)
In colloidal nanoparticle (NPs) devices, trap state densities at their surface exert a profound impact on the rate of charge carrier recombination and, consequently, on the deterioration of the device performance. Here, we report on the successful application of a ligand exchange strategy to effectively passivate the surface of cuprite (Cu2O) NPs. Cu2O NPs were prepared by means of a novel synthetic route based on flame spray pyrolysis. FTIR, XRD, XPS, and HRTEM measurements corroborate the formation of cubic cuprite Cu2O nanocrystals, excluding the possible presence of undesired CuO or Cu phases. Most importantly, steady-state emission and transient absorption assays document that surface passivation results in substantial changes in the intensity of emissive excitonic states-centered at copper and oxygen vacancies-and in the lifetime of excitons near the band edge. To shed light onto ultrafast processes in Cu2O nanocrystals additional pump probe experiments on the femtosecond and nanosecond time scales were carried out. Two discernible species were observed: on one hand, an ultrafast component ( ps) that relates to the excitons; on the other hand, a long-lived component ( μs) that originates from the defects/trap states.
Keywords: Engineering controlled terms: Nanocrystals; Spray pyrolysis Charge carrier recombination; Colloidal nanoparticles; Ligand passivation; Mercaptopropionic acid; Pump-probe experiments; Steady-state emissions; Surface passivation; Transient absorption Engineering main heading: Excitons EMTREE drug terms: 3 mercaptopropionic acid; copper; copper nanoparticle; nanocrystal; oxygen EMTREE medical terms: article; assay; infrared spectroscopy; pyrolysis; solid; steady state; surface property; transient absorption assay; transmission electron microscopy; X ray photoelectron spectroscopy

Effect of Fast Annealing on Structural Characteristics and Optical Properties of Cu2ZnSnS4 Absorber Films Deposited by Doctor-Blade Technique - Hassanien, A. E.; Abdelhaleem, Soraya; Ahmad, Rameez; Schuster, Matthias; Moustafa, S. H.; Distaso, Monica; Peukert, Wolfgang; Wellmann, Peter (Journal of Nanoelectronics and Optoelectronics, 2019)
Cu2ZnSnS4 of kesterite structure is a non-toxic, earth-abundant and low-cost alternative for Cu (In, Ga)Se-2 compound due to its direct band gap of similar to 1.5 eV and absorption coefficient higher than 10(4) cm(-1). The thin CZTS films were prepared by the Doctor-Blade technique as a cheap, simple and suitable process for large-scale production. The ink of CZTS nanoparticles was synthesized by a solvothermal method and dispersed in chloroform before deposition on glass substrates. The effect of annealing conditions (temperature and time) on the structural characteristics (phase formation and grain size) and optical properties (band gap) of CZTS thin films was investigated. The elemental composition of the CZTS films was investigated by energy dispersive X-ray spectroscopy. The films, before and after annealing, are rich in sulfur, which decreases with the increase of annealing temperature as a result of its evaporation at high temperature. X-ray diffraction analysis and Raman scattering measurements confirm the formation of the crystalline tetragonal phase of CZTS. Values of the optical band gap were estimated using Tauc equation and optical transmission data. The band gap decreases from 2.10 eV to 1.23 eV and the grain grows from 4.6 nm to 38.8 nm as the annealing temperature ascends. The dependence of band gap energy on the grain size is verified, thus, the size of the grain can be used as a factor tuning the band-gap energy.
CRIS-Team WoS Importer:2019-08-30

Effect of Growth Conditions on the Surface Morphology and Defect Density of CS-PVT-Grown 3C-SiC - Kollmuß, Manuel; La Via, Francesco; Wellmann, Peter (Crystal Research and Technology, 2023)
A systematic approach to determine the most crucial growth parameters and their effect on the surface morphology and defect density of sublimation grown (001) cubic silicon carbide (3C-SiC) is conducted. Close space physical vapor transport (CS-PVT) growth on 3C-SiC and 4° off oriented homoepitaxial chemical vapor deposition (CVD) grown seeding layers is performed. For each growth run, one growth parameter, e.g., temperature, pressure, or N2 flux is varied, while the other parameters are kept constant. Raman spectroscopy, potassium hydroxide (KOH) etching, as well as optical microscopy and atomic force microscopy (AFM) are used for the sample characterization. Step-flow-controlled growth is observed on all grown samples, while the stacking fault density is generally reduced with respect to the seeding layers. Increased temperature as well as increased pressure leads to roughening of the growth surface attributed to step bunching, while their effect on the stacking fault density seems to be only minor in the analyzed parameter range. Areas of strongly enhanced step bunching are present on all samples, and this effect is more pronounced at higher temperature and pressure. Increased nitrogen doping leads to a decreased stacking fault density but also increases the length of remaining stacking faults. The surface morphology is influenced by N2 on a macroscopic level rather than on microscopic scale.
CRIS-Team Scopus Importer:2023-05-26
Keywords: 3C-SiC; defect density; nitrogen doping; sublimation growth; surface morphology

Effect of Ligand Treatment on the Tuning of Infrared Plasmonic Indium Tin Oxide Nanocrystal Electrochromic Devices - Mashkov, Oleksandr; Körfer, Julien; Eigen, Andreas; Yousefi Amin, Amir-Abbas; Killilea, Niall Andrew; Barabash, Anastasia; Sytnyk, Mykhailo; Khansur, Neamul Hayet; Halik, Marcus; Webber, Kyle Grant; Heiß, Wolfgang (Advanced Engineering Materials, 2020)
Electrochromic devices operating in the near infrared are being developed as a part of smart windows that can dynamically modulate visible light and heat transmittance of solar irradiation, dependent on weather conditions and personal preferences. Here, doped metal oxide nanocrystals are used to obtain the desired effect in the infrared spectral region. Specifically, the infrared transmittance is electrochemically modulated by control of the carrier concentration in the nanocrystals. While indium tin oxide nanocrystals are already known to provide this effect, the consequence of ligand treatment during preparation of the nanocrystal electrode on the electrochromic properties is studied. The type of ligand treatment is shown to affect the surface morphology, as well as the localized plasmon resonance energy of the nanocrystal films. A short and convenient treatment by ethanedithiol cross-linking ligands is shown to provide superior results as compared with the formic acid treatment used in the previous work. Future work combining windows based on optimized electrochromic effects in the near infrared combined with those in the visible spectral range will simultaneously improve building energy efficiency and indoor human comfort.
CRIS-Team Scopus Importer:2020-05-02
Keywords: electrochromic windows; ligand exchange; localized surface plasmon resonances; metal oxide nanocrystals

Effect of Mg2+ content on lattice parameter and phase transformation temperature of β-α TCP - Götz-Neunhoeffer, Friedlinde; Neubauer, Jürgen; Göbbels, Matthias; Enderle, Ralph (European Cells & Materials, 2006)

Effect of PCBM on the photodegradation kinetics of polymers for organic photovoltaics - Distler, Andreas; Kutka, Peter; Sauermann, Tobias; Egelhaaf, Hans-Joachim; Guldi, Dirk Michael; Di Nuzzo, Daniele; Meskers, Stefan C. J.; Janssen, Rene A. J. (Chemistry of Materials, 2012)
The photo-oxidation behavior of three different polymers-namely, poly(3-hexylthiophene) (P3HT), poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2, 1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (C-PCPDTBT), and poly[2,6-(4,4-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-alt- 4,7-(2,1,3-benzothiadiazole)] (Si-PCPDTBT)-is investigated in neat polymer films and in blends with [6,6]-phenyl-C-butyric acid methyl ester (PCBM) for different polymer:PCBM ratios. PCBM is shown to have both stabilizing and destabilizing effects, the extent of which is dependent on the type of polymer with which it is blended. Screening of the polymer from incident light by PCBM turns out to play an only minor role in the stabilization of P3HT. Quenching of the polymer excited states is also not a significant stabilization mechanism, as demonstrated by the comparison of the reduction of photo-oxidation rates to the extent of photoluminescence quenching by PCBM and 2,7-dinitrofluorenone (DNF). Photoinduced absorption spectroscopy reveals that the enhanced degradation of C-PCPDTBT in blend films with PCBM correlates with the population of the polymer triplet state via the polymer:PCBM charge-transfer state. © 2012 American Chemical Society.

Effect of post-annealing treatment on the structure and luminescence properties of AIN: Tb3+ thin films prepared by radio frequency magnetron sputtering - Tucto Salinas, K. Y.; Flores Escalante, L. F.; Guerra Torres, J. A.; Grieseler, R.; Kups, T.; Pezoldt, J.; Osvet, Andres; Batentschuk, Miroslaw; Weingärtner, R. (Materials Science Forum, 2017)
Terbium-doped aluminum nitride thin films have been deposited by radio frequency magnetron sputtering. The influence of annealing treatments on structural, morphological and luminescence properties of the films is examined with the aim to optimize post-deposition annealing conditions. Temperatures starting from 500 up to 1000°C using two annealing techniques were investigated: rapid thermal processing and quartz tube furnace. X-ray diffraction analysis revealed the formation of aluminum oxide and aluminum oxynitride phases at temperatures higher than 750°C. The oxygen content in the surface layer was measured with energy dispersive X-ray. The terbium emission was obtained after excitation either by photons or electrons. The films treated with rapid thermal processing at 750°C resulted in the highest emissi
Keywords: Cathodoluminescence; Photoluminescence excitation; Aluminum nitride; Wide bandgap semiconductor; Rare earths; Terbium

Effect of the Precursor Chemistry on the Crystallization of Triple Cation Mixed Halide Perovskites - Singh, Mriganka; Abdelsamie, Maged; Li, Qihua; Kodalle, Tim; Lee, Do Kyoung; Arnold, Simon; Ceratti, Davide R.; Slack, Jonathan L.; Schwartz, Craig P.; Brabec, Christoph; Tao, Shuxia; Sutter-Fella, Carolin M. (Chemistry of Materials, 2023)
Triple cation, mixed halide perovskite compositions have been reported to be more thermally stable, exhibit fewer phase impurities, and show higher power conversion efficiency and better reproducibility than single cation perovskites. In this work, we explain the formation of Cs0.05FA0.81MA0.14Pb(I0.85Br0.15)3 via a multimodal in situ study combining structural information from synchrotron grazing-incidence wide-angle X-ray scattering (GIWAXS) and optical properties from photoluminescence (PL) spectroscopy with density functional theory calculations (DFT). The focus here is on the effects of the solvent and antisolvent during crystallization. The predominantly used solvents N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and the antisolvent chlorobenzene (CB) as well as the solvent-antisolvent-precursor interactions are investigated. Given the high elemental complexity and mutual interdependencies between solvent, antisolvent, and perovskite precursors, we found significant differences in the crystallization pathways. DMF-pure precursors show the formation of the DMF-containing intermediate phase and the nucleation of compositionally distinct perovskite phases, while when DMSO is added, only crystalline α- and δ-phases were found. In addition, the presence of DMSO helps the formation of α-perovskite. Coordination energy and bond order (BO) calculations support our experimental findings. Dripping of CB induces nucleation at room temperature, slows the α-phase formation rate, and appears to reduce the nucleation radius. These findings provide novel insights into solvent, antisolvent, and perovskite precursor interactions and their formation pathways. The complexity of interactions between solvents and reagents highlights the importance of understanding these effects to further improve the reproducibility and optimize processing conditions.
CRIS-Team Scopus Importer:2023-10-27

Effect of water vapor content during the solid state synthesis of manganese-doped magnesium fluoro-germanate phosphor on its chemistry and photoluminescent properties - Ali, Amjad; Chepyga, Liudmyla; Khanzada, Laraib Sarfraz; Osvet, Andres; Brabec, Christoph; Batentschuk, Miroslaw (Optical Materials, 2020)
Several samples of magnesium fluoro-germanate doped with Mn4+ were prepared by solid state synthesis with a different water vapor content in the synthesis atmosphere. A significant decrease in quantum yield and emission intensity was observed with the increase in water vapor content during synthesis. Although there was little effect on the emission spectra, the changes in excitation spectra indicate the dominance of magnesium germanate instead of magnesium fluoro-germanate at high water vapor content. X-ray diffraction (XRD) results show that the pure phase was only achieved with the least amount of water vapor. Refinement of XRD data estimates the quantities of different phases present. The effect on the grain size and morphology is also remarkable, as demonstrated by scanning electron microscopy imaging. The reason behind the changes is discussed in detail. The temperature dependence of the photoluminescence spectra was measured between room temperature and 500 °C where the luminescence is quenched to nearly 3% of its initial value.
CRIS-Team Scopus Importer:2019-12-17
Keywords: Effect of humidity; Magnesium fluoro-germanate; Photoluminescence; Solid state reaction; Thermographic phosphor; Water vapor

Effects of Alkyl Terminal Chains on Morphology, Charge Generation, Transport, and Recombination Mechanisms in Solution-Processed Small Molecule Bulk Heterojunction Solar Cells - Min, Jie; Luponosov, Yuriy N.; Gasparini, Nicola; Richter, Moses; Bakirov, Artem V.; Shcherbina, Maxim A.; Chvalun, Sergei N.; Grodd, Linda; Grigorian, Souren; Ameri, Tayebeh; Ponomarenko, Sergei A.; Brabec, Christoph (Advanced Energy Materials, 2015)
Length of the terminal alkyl chains at dicyanovinyl (DCV) groups of two dithienosilole (DTS) containing small molecules (DTS(Oct)2-(2T-DCV-Me)2 and DTS(Oct)2-(2T-DCV-Hex)2) is investigated to evaluate how this affects the molecular solubility and blend morphology as well as their performance in bulk heterojunction organic solar cells (OSCs). While the DTS(Oct)2-(2T-DCV-Me)2 (a solubility of 5 mg mL-1) system exhibits both high short circuit current density (J sc) and high fill factor, the DTS(Oct)2-(2T-DCV-Hex)2 (a solubility of 24 mg mL-1) system in contrast suffers from a poor blend morphology as examined by atomic force morphology and grazing incidence X-ray scattering measurements, which limit the photovoltaic properties. The charge generation, transport, and recombination dynamics associated with the limited device performance are investigated for both systems. Nongeminate recombination losses in DTS(Oct)2-(2T-DCV-Hex)2 system are demonstrated to be significant by combining space charge limited current analysis and light intensity dependence of current-voltage characteristics in combination with photogenerated charge carrier extraction by linearly increasing voltage and transient photovoltage measurements. DTS(Oct)2-(2T-DCV-Me)2 in contrast performs nearly ideal with no evidence of nongeminate recombination, space charge effects, or mobility limitation. These results demonstrate the importance of alkyl chain engineering for solution-processed OSCs based on small molecules as an essential design tool to overcome transport limitations.
Keywords: blend morphology; molecular solubility; organic solar cells; recombination dynamics; transport limitations

Effects of bridging atom and π-bridge length on physical and photovoltaic properties of A-π-D-π-A oligomers for solution-processed organic solar cells - Luponosov, Yuriy N.; Min, Jie; Bakirov, Artem V.; Dmitryakov, Petr V.; Chvalun, Sergei N.; Peregudova, Svetlana M.; Ameri, Tayebeh; Brabec, Christoph; Ponomarenko, Sergei A. (Dyes and Pigments, 2015)
Synthesis of novel acceptor-donor-acceptor oligomers with electron-withdrawing alkyldicyanovinyl groups linked through an oligothiophene π-bridge with either dithienosilole or cyclopentadithiophene electron donor units is described. Changing the bridgehead atom from carbon to silicon in the central donor unit leads to a significant change in optical, thermal and structural properties of the oligomers. In addition, elongation of the oligothiophene π-bridge in the oligomers increases energies of HOMO and LUMO levels and leads to an unexpected hypsochromic shift of their absorption spectrum, because extension of the conjugation length cannot compensate a decrease of the intramolecular charge transfer between the dithienosilole and dicyanovinyl units. Although these minor changes in the chemical structures have a pronounced impact on the morphologies of their blends with PC70BM, the optimized solution-processed organic solar cells based on these small molecules demonstrate similar power conversion efficiencies.
EAM Import::2019-03-14
Keywords: Alkyldicyanovinyl groups; Dithienosilole; Donor-acceptor oligomers; Effect of heteroatom substitution; Oligothiophenes; Organic solar cells

Effects of bridging atom in donor units and nature of acceptor groups on physical and photovoltaic properties of A-π-D-π-A oligomers - Min, Jie; Luponosov, Yuriy N.; Khanin, Dmitry A.; Dmitryakov, Petr V.; Svidchenko, Evgeniya A.; Peregudova, Svetlana M.; Grodd, Linda; Grigorian, Souren; Chvalun, Sergei N.; Ponomarenko, Sergei A.; Brabec, Christoph (Organic Electronics, 2018)
The synthesis of a series of novel A-π-D-π-A oligomers bearing either electron-donating dithieno[3,2-b:2′,3′-d]silole (DTS) or dithieno[3,2-b:2′,3′-d]pyrrole (DTP) units linked through a bithiophene π-bridge with the electron-withdrawing methyldicyanovinyl (DCV) or N-ethylrhodanine (Rh) groups is described. In order to evaluate the effects of different donor-acceptor combinations on various physical properties of the oligomers they are comprehensively studied by UV–Vis spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cyclic voltammetry (CV). Replacing the DTS by DTP as well as the DCV by Rh leads to increasing of HOMO energy levels and slight decreasing of LUMO energy levels. The DTP-based oligomers have a red shift in absorption spectra and an increased solubility as compared to the DTS-based analogs. Replacing the acceptor DCV unit by Rh also results in significantly higher solubility, but the Rh-based oligomers exhibit weaker intermolecular interactions, poorer optical absorption of sun light as well as lower charge carrier mobility in blends. Altogether, the structural improvement of the DTS-DCV and DTP-DCV blends upon annealing correlates well with the observed photovoltaic performances in organic solar cells. These results give more insight how to fine-tune and predict physical properties and photovoltaic performance of small A-π-D-π-A molecules having different donor-acceptor combinations in their chemical structures and thus providing a molecular design guideline for the next generation of high-performance photovoltaic materials
Keywords: Electron-donating; Electron-withdrawing; Oligomers; Organic solar cells; Posttreatment methods; Power conversion efficiencies; Solvent vapor annealing; Thermal annealing

Effects of electron-withdrawing group and electron-donating core combinations on physical properties and photovoltaic performance in D-π-A star-shaped small molecules - Luponosov, Yuriy N.; Min, Jie; Solodukhin, Alexander N.; Kozlov, Oleg V.; Obrezkova, Marina A.; Peregudova, Svetlana M.; Ameri, Tayebeh; Chvalun, Sergei N.; Pshenichnikov, Maxim S.; Brabec, Christoph; Ponomarenko, Sergei A. (Organic Electronics, 2016)
The first representatives of star-shaped molecules having 3-alkylrhodanine (alkyl-Rh) electron-withdrawing groups, linked through bithiophene π-spacer with electron-donating either triphenylamine (TPA) or tris(2-methoxyphenyl)amine (m-TPA) core were synthesized. The physical properties and photovoltaic performance of these novel molecules with 3-ethylrhodanine groups were comprehensively studied and compared to their full analogs having dicyanovinyl (DCV) units as the other type of well-known and frequently used acceptor groups. On one hand, the former demonstrate several advantages such as higher solubility and better photovoltaic performance in bulk-heterojunction (BHJ) organics solar cells (OSCs) as compared to the latter. Nevertheless, the former have slightly lower optical/electrochemical bandgaps and higher thermooxidation stability. On the other hand, molecules of both series based on m-TPA core along with higher solubility and higher position of HOMO energy levels have more pronounced tendency to crystalize as compared to the TPA-based molecules. Detailed investigation of the structure-property relationships for these series of molecules revealed that donor and acceptor unit combinations influence both charge generation and charge transport/recombination properties, as demonstrated by the ultrafast photoinduced absorption spectroscopy, space charge limited current measurements and transient photovoltage technique. These results give more insight how to fine-tune and predict physical properties and photovoltaic performance of small molecules having either alkyl-Rh or DCV units in their chemical structures and thus providing a molecular design guideline for the next generation of high-performance photovoltaic materials.
EAM Import::2019-03-14
Keywords: 3-Ethylrhodanine; Dicyanovinyl; Organic solar cells; Star-shaped molecules; Triphenylamine; Ultrafast charge separation

Effects of Fluorination on Fused Ring Electron Acceptor for Active Layer Morphology, Exciton Dissociation, and Charge Recombination in Organic Solar Cells - Hou, Licheng; Lv, Jie; Wobben, Friso; Le Corre, Vincent Marc; Tang, Hua; Singh, Ranbir; Kim, Min; Wang, Fufang; Sun, Haitao; Chen, Wenjing; Xiao, Zhengguo; Kumar, Manish; et al. (ACS Applied Materials and Interfaces, 2020)
Fluorination is one of the effective approaches to alter the organic semiconductor properties that impact the performance of the organic solar cells (OSCs). Positive effects of fluorination are also revealed in the application of fused ring electron acceptors (FREAs). However, in comparison with the efforts allocated to the material designs and power conversion efficiency enhancement, understanding on the excitons and charge carriers' behaviors in high-performing OSCs containing FREAs is limited. Herein, the impact of fluorine substituents on the active layer morphology, and therefore exciton dissociation, charge separation, and charge carriers' recombination processes are examined by fabricating OSCs with PTO2 as the donor and two FREAs, O-IDTT-IC and its fluorinated analogue O-IDTT-4FIC, as the acceptors. With the presence of O-IDTT-4FIC in the devices, it is found that the excitons dissociate more efficiently, and the activation energy required to split the excitons to free charge carriers is much lower; the charge carriers live longer and suffer less extent of trap-assisted recombination; the trap density is 1 order of magnitude lower than that of the nonfluorinated counterpart. Overall, these findings provide information about the complex impacts of FREA fluorination on efficiently performed OSCs.
Keywords: fluorination; exciton dissociations; activation energy; trap assisted recombination; crystallinity

Effects of oligothiophene π-bridge length on physical and photovoltaic properties of star-shaped molecules for bulk heterojunction solar cells - Min, Jie; Luponosov, Yuriy N.; Baran, Derya; Chvalun, Sergei N.; Shcherbina, Maxim A.; Bakirov, Artem V.; Dmitryakov, Petr V.; Peregudova, Svetlana M.; Kausch-Busies, Nina; Ponomarenko, Sergei A.; Ameri, Tayebeh; Brabec, Christoph (Journal of Materials Chemistry A, 2014)
The preparation of four different star-shaped donor (D)-π-acceptor (A) small molecules (N(Ph-1T-DCN-Me)3, N(Ph-2T-DCN-Me)3, N(Ph-2T-DCN-Hex)3 and N(Ph-3T-DCN-Hex)3) possessing various oligothiophene π-bridge lengths and their use in solution-processed bulk heterojunction small molecule solar cells is reported. Optical and electrochemical data show that increasing oligothiophene π-bridge length leads to a decrease of the optical band gap due to a parallel increase of the highest occupied molecular orbital (HOMO) level. Furthermore, subtle modifications of a molecular π-bridge length strongly affect the thermal behavior, solubility, crystallization, film morphology and charge carrier mobility, which in turn significantly change the device performance. Although the moderately increasing oligothiophene π-bridge length uplifts the HOMO level, it nevertheless induces an increase of the efficiency of the resulting solar cells due to a simultaneous improvement of the short circuit current (Jsc) and fill factor (FF). The study demonstrates that such an approach can represent an interesting tool for the effective modulation of the photovoltaic properties of the organic solar cells (OSCs) at a moderate cost.
EAM Import::2019-03-14
Keywords: Bulk heterojunction solar cells; Oligothiophenes; Photovoltaic property; Star-shaped molecules

Effects of source material on epitaxial growth of fluorescent SiC - Jokubavicius, V.; Hens, Philip; Liljedahl, R.; Sun, J. W.; Kaiser, Michl; Wellmann, Peter; Sano, S.; Yakimova, R.; Kamiyama, S.; Syväjärvi, Mikael (Thin Solid Films, 2012)
The growth of fluorescent SiC using Fast Sublimation Growth Process was demonstrated using different types of SiC source materials. These were prepared by (i) high-temperature hot pressing, (ii) chemical vapor deposition and (iii) physical vapor transport. The optimized growth rates of 50 mu m/h, 170 mu m/h and 200 mu m/h were achieved using the three types of sources, respectively. The best results in respect to growth rates are obtained using higher density sources. Fluorescent SiC layers with mirror-like morphology, very good crystal quality and yellowish or warm white light photoluminescence at room temperature were grown using all three types of the source materials. (C) 2011 Elsevier B. V. All rights reserved.
Keywords: Sublimation growth; Fluorescence; Photoluminescence; Silicon carbide

Effects on Photovoltaic Characteristics by Organic Bilayer- And Bulk-Heterojunctions: Energy Losses, Carrier Recombination and Generation - Lee, Tack Ho; Park, Song Yi; Du, Xiaoyan; Park, Sujung; Zhang, Kaicheng; Li, Ning; Cho, Shinuk; Brabec, Christoph; Kim, Jin Young (ACS Applied Materials and Interfaces, 2020)
We investigate the photovoltaic characteristics of organic solar cells (OSCs) for two distinctly different nanostructures, by comparing the charge carrier dynamics for bilayer- and bulk-heterojunction OSCs. Most interestingly, both architectures exhibit fairly similar power conversion efficiencies (PCEs), reflecting a comparable critical domain size for charge generation and charge recombination. Although this is, at first hand, surprising, a detailed analysis points out the similarity between these two concepts. A bulk-heterojunction architecture arranges the charge generating domains in a 3D ensemble across the whole bulk, while bilayer architectures arrange the specific domains on top of each other, rather than sharp bilayers. Specifically, for the polymer PBDB-T-2F, we find that the enhanced charge generation in a bulk composite is partially compensated by reduced recombination in the bilayer architecture, when nonfullerene acceptors (NFAs) are used instead of a fullerene acceptor. Overall, we demonstrate that bilayer-heterojunction OSCs with NFAs can reach competitive PCEs compared to the corresponding bulk-heterojunction OSCs because of reduced nonradiative open-circuit voltage losses, and suppressed trap-assisted recombination, as a result of a vertically separated donor-to-acceptor nanostructure. In contrast, the bilayer-heterojunction OSCs with the fullerene acceptor exhibited poor photovoltaic characteristics compared to the corresponding bulk devices because of highly aggregated acceptor molecules on top of the polymer donor. Although free carrier generation is reduced in a in a bilayer-heterojunction, because of reduced donor/acceptor interfaces and a limited exciton diffusion length, more favorable transport pathways for unipolar charge collection can partially compensate the aforementioned disadvantages. We propose that the unique properties of NFAs may open a technical venue for the bilayer-heterojunction as a great and easy alternative to the bulk heterojunction.
CRIS-Team Scopus Importer:2020-12-25
Keywords: carrier behavior; energy loss; nonfullerene small molecular acceptor; organic nanostructure; organic solar cell

Efficiency Limits and Color of Semitransparent Organic Solar Cells for Application in Building-Integrated Photovoltaics - Forberich, Karen; Guo, Fei; Bronnbauer, Carina; Brabec, Christoph (Energy Technology, 2015)
We have modified the well-known Scharber model for the efficiency limits of organic solar cells for the case of semitransparent devices, which are considered as one of the most promising applications for this photovoltaic (PV) technology. We introduce a modified external quantum efficiency (EQE) relation and derive the transparency from the convolution of the calculated transmittance spectrum with the human eye sensitivity. We find that the design guidelines for the optimum band gap of the absorber material have to be carefully adapted for the desired transparency, especially for transparency values exceeding 40%. In addition, we examine the relationship between efficiency, transmitted color, and band gap and conclude that high efficiencies can be achieved for a wide range of colors. Our model shows good agreement with experimental values from the literature and can be easily adapted to different applications (e.g., greenhouses) by using the appropriate spectrum. © 2015 WILEY-VCH Verlag GmbH & Co.
Keywords: Building-integrated photovoltaics; Organic solar cells; Photovoltaics; Scharber model; Semitransparency

Efficient Double- and Triple-Junction Nonfullerene Organic Photovoltaics and Design Guidelines for Optimal Cell Performance - Firdaus, Yuliar; Ho, Carr Hoi Yi; Lin, Yuanbao; Yengel, Emre; Le Corre, Vincent Marc; Nugraha, Mohamad I; Yarali, Emre; So, Franky; Anthopoulos, Thomas D (ACS Energy Letters, 2020)
The performance of multijunction devices lags behind single-junction organic photovoltaics (OPVs) mainly because of the lack of suitable subcells. Here, we attempt to address this bottleneck and demonstrate efficient nonfullerene-based multijunction OPVs while at the same time highlighting the remaining challenges. We first demonstrate double-junction OPVs with power conversion efficiency (PCE) of 16.5%. Going a step further, we developed triple-junction OPVs with a PCE of 14.9%, the highest value reported to date for this triple-junction cells. Device simulations suggest that improving the front-cell's carrier mobility to >5 X 10(-4) cm(2) V-1 s(-1) is needed to boost the efficiency of double- and triple-junction OPVs. Analysis of the efficiency limit of triple-junction devices predicts that PCE values of close to 26% are possible. To achieve this, however, the optical absorption and charge transport within the subcells would need to be optimized. The work is an important step toward next-generation multijunction OPVs.

Efficient Exciton Diffusion in Organic Bilayer Heterojunctions with Nonfullerene Small Molecular Acceptors - Lee, Tack Ho; Park, Song Yi; Park, Won-Woo; Du, Xiaoyan; Son, Jae Hoon; Li, Ning; Kwon, Oh-Hoon; Woo, Han Young; Brabec, Christoph; Kim, Jin Young (ACS Energy Letters, 2020)
Solution-processed bilayer organic solar cells (OSCs) with high performance are demonstrated for nonfullerene small molecular acceptors (NFAs). Unlike fullerene acceptors, NFAs show significant spectral overlap between their absorption and the photoluminescence (PL) of a polymer donor, which makes the design of an efficient exciton-harvesting bilayer heterojunction possible. Efficient exciton diffusion in the organic bilayer heterojunction is realized by long-range energy transfer between a polymer donor and NFAs. We observed efficient exciton diffusion from the polymer/NFA bilayer heterojunctions via thickness-dependent PL quenching and time-resolved PL measurements. Despite the strongly reduced donor-acceptor interface area, a substantial density of charge-transfer states is observed for the polymer/NFA bilayer heterojunctions by electroluminescence measurements. Overall, polymer/NFA bilayer heterojunction OSCs demonstrate a power conversion efficiency of 9%-10%, which is comparable to the photovoltaic performance of bulk heterojunction OSCs, with the additional advantage of simplified microstructure formation.
Created from Fastlane, WoS look-up

Efficient Image Segmentation for Detection of Dislocations in High Resolution Light Microscope Images of SiC Wafers - Karpinski, Harald; Sakwe, Aloysius; Fried, Michael J.; Bänsch, Eberhard; Wellmann, Peter (Materials Science Forum, 2011)
The determination of dislocation density and in particular the dislocation distribution in SiC wafers is of particular interest for SiC crystal growth development and production. We present an image recognition tool allowing the wafer analysis with specific needs for SiC. In the first stage of expansion, micropipes are selected and counted from SiC wafers that have been etched by KO
Keywords: image analysis; dislocations; SiC; automatic detection

Efficient Organic Solar Cells with Extremely High Open-Circuit Voltages and Low Voltage Losses by Suppressing Nonradiative Recombination Losses - Liu, Xi; Du, Xiaoyan; Wang, Junyi; Duan, Chunhui; Tang, Xiaofeng; Heumüller, Thomas; Liu, Guogang; Li, Yan; Wang, Zhaohui; Wang, Jing; Liu, Feng; Li, Ning; et al. (Advanced Energy Materials, 2018)
One of the most important factors that limits the efficiencies of bulk-heterojunction organic solar cells (OSCs) is the modest open-circuit voltage (Voc) due to their large voltage loss (Vloss) caused by significant nonradiative recombination loss. To boost the performance of OSCs toward their theoretical limit, developing high-performance donor: acceptor systems featuring low Vloss with suppressed nonradiative recombination losses (<0.30 V) is desired. Herein, high performance OSCs based on a polymer donor benzodithiophene-difluorobenzoxadiazole-2-decyltetradecyl (BDT-ffBX-DT) and perylenediimide-based acceptors (PDI dimer with spirofluorene linker (SFPDI), PDI4, and PDI6) are reported which offer a high power conversion efficiency (PCE) of 7.5%, 56% external quantum efficiency associated with very high Voc (>1.10 V) and low Vloss (<0.60 V). A high Voc up to 1.23 V is achieved, which is among the highest values reported for OSCs with a PCE beyond 6%, to date. These attractive results are benefit from the suppressed nonradiative recombination voltage loss, which is as low as 0.20 V. This value is the lowest value for OSCs so far and is comparable to high performance crystalline silicon and perovskite solar cells. These results show that OSCs have the potential to achieve comparable Voc and voltage loss as inorganic photovoltaic technologies. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Keywords: Nonfullerene acceptors; Nonradiative recombination losses; Voltage losses; Open-circuit voltages; Organic solar cells

Efficient Polymer Solar Cells Based on Non-fullerene Acceptors with Potential Device Lifetime Approaching 10 Years - Du, Xiaoyan; Heumüller, Thomas; Gruber, Wolfgang; Classen, Andrej; Unruh, Tobias; Li, Ning; Brabec, Christoph (Joule, 2019)
Organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) have developed very fast in recent years. A proper balance among power conversion efficiency (PCE), stability, and production cost needs further elaboration. Here we investigate the industrial viability of highly efficient OSCs based on several representative NFAs. The most stable OSCs exhibit PCE of ∼8% along with extrapolated T 80 lifetime (80% of the initial PCE) of over 11,000 hr under equivalent 1 sun illumination, which would lead to a very impressive operational lifetime approaching 10 years. Photo-stability is strongly dependent on the end-group and side-chain engineering of the NFAs. Breaking of conjugation during photo-aging leads to increased energetic traps. Fluorination of the end-group stabilizes molecules against light soaking, while adding methyl groups shows an opposite trend. Side-chain modification can significantly influence the morphological stability. Reducing synthetic complexity of this class of NFAs will ultimately push the organic photovoltaics technology into real-life applications. © 2018 Elsevier Inc. We investigate the industrial viability of highly efficient organic solar cells (OSCs) based on several representative non-fullerene acceptors (NFAs) by taking into consideration the three essential parameters: power conversion efficiency, photo-stability, and materials cost. End-group and side-chain modifications of NFAs strongly influence long-term photo-stability. Promising extrapolated operational lifetime approaching 10 years has been demonstrated with the most stable system. Industrial figure of merit (i-FoM) analysis highlights the importance of lowering the synthetic complexity of the NFAs for commercialization of this technology. © 2018 Elsevier Inc. Organic solar cells with non-fullerene acceptors (NFAs) have developed rapidly in recent years. Breakthroughs in power conversion efficiency (PCE) have significantly raised the confidence in the community for commercialization of this technology. In the phase of developing new materials via molecular engineering, more attention should be paid on industrial figure of merit (i-FoM), which considers the balance of PCE, stability, and production cost. Here we investigate industrial viability of highly efficient organic solar cells based on several representative NFAs. Molecular engineering on both end-groups and side chains significantly influences the long-term stability of organic solar cells by altering the intrinsic chemical stability of the molecules under light soaking as well as morphological stability. Promising lifetime approaching 10 years is demonstrated in stable candidates. Reducing synthetic complexity is highlighted in order to push this technology into real-life appli
Keywords: non-fullerene acceptors; organic photovoltaics; device operational stability; industrial figure of merit; bulk-heterojunction morphology

Efficient Semitransparent Organic Solar Cells with CRI over 90% Enabled by an Ultralow-Bandgap A-DA'D-A Small Molecule Acceptor - Xu, Xiang; Wei, Qingya; Zhou, Zhisheng; He, Haozhe; Tian, Jingjing; Yip, Hin Lap; Fu, Yuang; Lu, Xinhui; Zhou, Yonghua; Li, Yongfang; Zou, Yingping (Advanced Functional Materials, 2023)
Semitransparent organic solar cells (ST-OSCs) can function as power-generating windows due to their ability to allow visible light go-through for human eyesight while absorbing low-energy photons in the near-infrared region for photocurrent generation. In this regard, effective ST-OSCs with high light utilization efficiency (LUE) and color rendering index (CRI) can be developed via a synergistic material and device engineering strategy. Herein, an A-DA'D-A acceptor BZO-4Cl is synthesized with an ultralow optical bandgap of 1.26 eV and bathochromically shifted absorption of roughly 60 nm with respect to Y6. Initially, the opaque devices using PTB7-Th as the donor show a high power conversion efficiency (PCE) of 14.12%, which can be listed as one of the highest efficiencies for the PTB7-Th-based OSCs so far. Then, through these efforts of optimizations in the bulk-heterojunction(BHJ) composition, top electrodes and anti-reflection layer, the cutting-edge ST-OSC demonstrates a high LUE of 4.02%, and a CRI of 90.67%, making it one of the best-performing ST-OSCs with both high LUE and CRI values. These results indicate that the ST-OSCs presented in this study have significant potential for use in applications that possess transparent visible light and energy-generation functions.
CRIS-Team Scopus Importer:2023-09-29
Keywords: color rendering indexes; light utilization efficiency; low-bandgap acceptors; optical modeling; semitransparent organic solar cells

Efficient, stable, and fully printed carbon-electrode perovskite solar cells enabled by hole-transporting bilayers - Du, Tian; Qiu, Shudi; Zhou, Xin; Le Corre, Vincent Marc; Wu, Mingjian; Dong, Lirong; Peng, Zijian; Zhao, Yicheng; Jang, Dongju; Spiecker, Erdmann; Brabec, Christoph; Egelhaaf, Hans-Joachim (Joule, 2023)
Printable planar carbon electrodes emerge as a promising replacement for thermally evaporated metals as the rear contact for perovskite solar cells (PSCs). However, the power conversion efficiencies (PCEs) of the state-of-the-art carbon-electrode PSC (c-PSC) noticeably lag behind their metal-electrode counterparts. Here, we propose a hole-transporting bilayer (HTbL) configuration to improve the fill factor and the open-circuit voltage of c-PSCs simultaneously. The HTbL is prepared by sequentially blade coating two organic semiconductors between perovskite and carbon, with the outer HTL enhancing hole extraction to carbon, while the inner HTL mitigates perovskite surface recombination. Consequently, our fully printed c-PSCs with HTbL outperform those with single HTL, and a stabilized champion PCE of 19.2% is achieved compared with that of 17.3%. Our prototype c-PSC stably operates during 1 sun, 65°C aging test (ISOS-L-2I) for 2,500 h showing negligible PCE drop, validating its potential as a highly cost-effective photovoltaic technology.
CRIS-Team Scopus Importer:2023-08-18
Keywords: bilayer; carbon electrode; fully printed perovskite solar cells; hole transporting; stability

Efficient Surface Passivation and Electron Transport Enable Low Temperature-Processed Inverted Perovskite Solar Cells with Efficiency over 20% - Wang, Helin; Yang, Fu; Li, Ning; Kamarudin, Muhammad Akmal; Qu, Junle; Song, Jun; Hayase, Shuzi; Brabec, Christoph (ACS Sustainable Chemistry & Engineering, 2020)
PCBM is a fullerene derivative, which is commonly employed as an electron transport layer (ETL), and still has some issues to fabricate low temperature-processed perovskite solar cells (PSCs) such as surface trap states, low electron mobility, and extra recombination losses at the perovskite/PCBM interface. Herein, a novel perylene diimide dimer (2FBT2FPDI) is synthesized and employed as an ETL or intermediary layer to overcome these challenges. Owing to its suitable energy levels and high electron mobility, 2FBT2FPDI shows great potential to serve as a promising efficient ETL in the photovoltaic devices. Moreover, 2FBT2FPDI can coordinate with the lead site of the perovskite surface, which helps to heal the surface defects and suppress charge-trapped recombination. Therefore, the performance of PSCs is greatly improved from 17.3 to 20.3%, when 2FBT2FPDI was used as the intermediary layer to assist the growth of the PCBM film. This work presents a new direction through interface engineering with n-type nonfullerene small molecules for low temperature-processed stable and highly efficient inverted PSCs.<br
Keywords: perovskite solar cell; surface passivation; electron transport material; high efficiency; device stability

Einfluss Ca-reicher Additive in Verbindung mit Li2CO3 auf das Hydratationsverhalten von Monocalciumaluminat - Enderle, Ralph; Neubauer, Jürgen; Götz-Neunhoeffer, Friedlinde (GDCh-Monographien, 2004)
UnivIS-Import:2015-03-09:Pub.2004.nat.dgeo.IGM.LM.einflu_4

Electrical and optical characterization of p-type boron-doped 6H-SiC bulk crystals - Bickermann, Matthias; Weingärtner, Roland; Herro, Ziad Georges; Hofmann, Heinz-Dieter; Künecke, Ulrike; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2003)
Electrical and optical characterization was performed to obtain information about the doping and compensation levels of samples cut from boron doped, physical vapor transport (PVT) grown 6H-SiC crystals. Values for N-A and N-D can be derived from analysis on temperature dependent Hall effect measurement data. The charge carrier concentration p at room temperature depends approximately linearly on N-A/N-D. The below band-gap absorption (BBGA) maximum at about 730 nm is correlated mainly to N-A, and, for constant N-A, is slightly anti-correlated to N-D. The same results can be obtained from an rootalpha vs. E plot extrapolated to alpha = 0 in the near band-gap region, as the broad absorption band induces a shift in the optically detected band-gap towards lower energies. Absorption measurements can give an estimation of N-A-N-D in boron doped SiC samples, and from wafers cut from the same crystal, the concentration of boron and compensating impurities can be evaluate
Keywords: Boron Doping; Hall-Effect; Homogeneous Incorporation; Optical Absorption; Optically Determined Band-Gap; p-Type SiC

Electrical-Field-Driven Tunable Spectral Responses in a Broadband-Absorbing Perovskite Photodiode. - Tang, Xiaofeng; Matt, Gebhard; Gao, Shuai; Gu, Ening; Almora, Osbel; Brabec, Christoph (ACS Applied Materials and Interfaces, 2019)
Controllably manipulating the spectral response of broadband-absorbing semiconductors is crucial for developing wavelength-selective optoelectronic devices. In this article, we report for the first time, the bias-dependent spectral responses for a metal-halide perovskite photodiode. Tunable external quantum efficiencies in the short- and long-wavelength regimes, and the full spectral range (ca. 300-800 nm) are observed when the device is operated under short-circuit, and forward and reverse bias conditions, respectively. This observation is understood by the interplay of wavelength-dependent penetration depth and barrier formation within the photodiode device stack. The general applicability of this concept is confirmed by a systematic study on a series of mixed-halide perovskite devices. These results suggest that the proposed concept allows as a promising platform and should inspire further exploration of multispectral responsive optoelectronic devices.
Keywords: perovskite; optoelectronics; electrodeposition; mixed-halide perovskite; external quantum efficiency

Electrical, optical and morphological properties of nanoparticle indium-tin-oxide layers - Groß, Michael; Winnacker, Albrecht; Wellmann, Peter (Thin Solid Films, 2007)
Porous layers were prepared from DEGUSSA's ITO (In2O3:Sn) nanoparticle dispersion by doctor blading followed by annealing in air. We investigated the influence of various annealing parameters on electrical, optical and morphological thin film properties. Conductance rises with increasing annealing temperature and time by more than three orders of magnitude up to 44 Omega(-1) cm(-1). Besides this we found an abrupt decrease in free charge carrier concentration above a critical annealing temperature of 250 degrees C, which leads to a step in conductance curve. In spite of particle growing during annealing no decrease in porosity was observed and in opposite to compact material, nanoparticle layers do not exhibit an appreciable shrinkage below recrystallisation temperature. These both indicate a densification hindering particle pinning effect, which is believed to be currently the main obstruction to achieve higher electrical conductivities. (c) 2007 Elsevier B.V All rights reserved.
Keywords: Indium–tin–oxide; ITO; Nanoparticle; Conductance; Transmittance; Porosity; Transport; Cluster

Electrical properties of pSi/[6,6] phenyl-C61 butyric acid methyl ester/Al hybrid heterojunctions: Experimental and theoretical evaluation of diode operation - Bednorz, Mateusz; Fromherz, Thomas; Matt, Gebhard; Brabec, Christoph; Scharber, Markus; Sariciftci, N. Serdar (Journal of Applied Physics, 2012)
In this work, we analyze electrically the Al/p-Si/[6,6] phenyl-C61 butyric acid methyl ester/Al hybrid heterojunction. The barrier height at the p-Si/PCBM interface corresponding to the difference between Si valence band edge and the lowest unoccupied molecular orbital energy level of PCBM is studied with current-voltage (J-V) and capacitance-voltage (C-V) methods and determined to be ≃ 0.55eV. This value is in agreement with the onset energy of spectrally resolved photocurrent measurements presented in a previous publication [Matt, Adv. Mater. 22, 647 (2010)]. For the J-V characteristics, a thorough model based on an interface generation-recombination current is proposed. All relevant energy levels for this model are obtained experimentally. As origin of the large reverse current, the thermal generation of charge carriers throughout the Si depletion region is identified by the thermal activation measurements. © 2012 American Institute of Physics.

Electroluminescence imaging of organic photovoltaic modules - Hoyer, U.; Wagner, M.; Swonke, Th.; Bachmann, J.; Auer, R.; Osvet, Andres; Brabec, Christoph (Applied Physics Letters, 2010)
We report on electroluminescence (EL) imaging of organic photovoltaic cells and modules with poly(3-hexylthiophene)/[6,6]-phenyl C61 butyric acid methyl ester as semiconductor layer. The dominant EL emission is found in a spectral regime between 1200 and 1400 nm and is identified as the radiative decay of the charge transfer complex formed between the polymer and the fullerene. Electroluminescence emission from the pristine compounds is either much weaker or completely absent. Overall, electroluminescence imaging is shown to give valuable information on the defects but also on the performance of organic solar modules. © 2010 American Institute of Physics.

Electron barrier formation at the organic-back contact interface is the first step in thermal degradation of polymer solar cells - Sachs-Quintana, I. T.; Heumüller, Thomas; Mateker, William R.; Orozco, Darian E.; Cheacharoen, Rongrong; Sweetnam, Sean; Brabec, Christoph; Mcgehee, Michael D. (Advanced Functional Materials, 2014)
Long-term stability of polymer solar cells is determined by many factors, one of which is thermal stability. Although many thermal stability studies occur far beyond the operating temperature of a solar cell which is almost always less than 65 °C, thermal degradation is studied at temperatures that the solar cell would encounter in real-world operating conditions. At these temperatures, movement of the polymer and fullerenes, along with adhesion of the polymer to the back contact, creates a barrier for electron extraction. The polymer barrier can be removed and the performance can be restored by peeling off the electrode and depositing a new one. X-ray photoelectron spectroscopy measurements reveal a larger amount of polymer adhered to electrodes peeled from aged devices than electrodes peeled from fresh devices. The degradation caused by hole-transporting polymer adhering to the electrode can be suppressed by using an inverted device where instead of electrons, holes are extracted at the back metal electrode. The problem can be ultimately eliminated by choosing a polymer with a high glass transition temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Keywords: degradation; interfaces; lifetime; organic photovoltaics; stability

Electronic Raman Studies of Shallow Donors in Silicon Carbide - Püsche, Roland; Hundhausen, Martin; Ley, Lothar; Semmelroth, Kurt; Pensl, Gerhard; Desperrier, Patrick; Wellmann, Peter; Haller, Eugene E.; Ager, J.W.; Starke, Ulrich (Materials Science Forum, 2006)
We study electronic Raman scattering of phosphorus and nitrogen doped silicon carbide (SiC) as a function of temperature in the range 7 K < T < 300K. We observe a series of peaks in the Raman spectra which we assign to electronic transitions at nitrogen and phosphorus donors on different lattice sites. These transitions are identified as valley orbit transitions of the Is donor ground state. From the polarization dependence of the observed peaks, we find that all electronic Raman signals have E2-symmetry of C 6v for the hexagonal polytypes (6H-SiC and 4H-SiC) and E-syinmetry of C3., for 15R-SiC. Wc find a reduction of the intensities of all valley-orbit Raman signals with increasing temperature and ascribe this reduction to the decreasing occupation of donor state
UnivIS-Import:2015-04-14:Pub.2006.nat.dphy.IAP.LAP.electr
Keywords: Doping; Nitrogen-donor; Phosphorus-donor; Raman spectroscopy

Electronics Production: Research from Materials to Systems, Proceedings of the 2nd Chinese-German Summer School in Shanghai - Wellmann, Peter; Feng, Zhibiao; Shi, Guoyong (Tongji University Press, 2007)

Electronic states tuning of InAs self-assembled quantum dots - Garcia, J.M.; Mankad, T.; Holtz, O.; Wellmann, Peter; Petroff, P.M. (Applied Physics Letters, 1998)
We demonstrate the dimensional tuning of InAs self-assembled quantum dots (QDs) by changing the growth kinetics during the capping of InAs islands with GaAs. Modifying the growth sequence during the capping of InAs islands, allows us to tune the thickness and lateral dimensions of the QDs while keeping the wetting layer thickness constant. Using the same method but embedding the tuned InAs islands into AlAs layers allows to further blueshift the photoluminescence emission to higher energies while keeping the wetting layer thickness constant. The main process responsible for the QDs size modification is consistent with a kinetically controlled materials redistribution of the InAs islands that minimizes the energy of the epitaxial layers at the start up of the GaAs capping deposition.<br

Elucidating How Low Energy Offset Matters to Performance of Nonfullerene Acceptor-Based Solar Cells - Tokmoldin, Nurlan; Sun, Bowen; Moruzzi, Floriana; Patterson, Acacia; Alqahtani, Obaid; Wang, Rong; Collins, Brian A.; McCulloch, Iain; Lüer, Larry; Brabec, Christoph; Neher, Dieter; Shoaee, Safa (ACS Energy Letters, 2023)
The energetic offset between the highest occupied molecular orbitals of the donor and acceptor components of organic photovoltaic blends is well-known to affect the device efficiency. It is well-established that a decreasing offset increases the open-circuit voltage but reduces the short-circuit current, which has been explained by insufficient exciton dissociation. However, the impact of the offset on the fill factor and underlying processes is less clear. Here, we study free charge generation and recombination in three different nonfullerene acceptors, Y6, ITIC, and o-IDBTR, blended with the same donor polymer PM6. We demonstrate that a diminishing offset results in field-dependent charge generation related to field-assisted exciton dissociation. On the other hand, reformation of excitons from free charges is identified as an additional channel for charge recombination, which goes along with a substantial rise in the bimolecular recombination coefficient. In combination of these two effects, the fill factor drops considerably with a decreasing energy offset. Using the comparison between PM6:ITIC and PM6:o-IDBTR, we show that bulk properties such as morphology and carrier mobilities can not fully explain the observed difference in performance, highlighting the importance of interfacial kinetics and thermodynamics in controlling the device efficiency, both through generation and recombination of charge carriers.
CRIS-Team Scopus Importer:2023-07-14

Elucidating the Excited-State Properties of CuInS2 Nanocrystals upon Phase Transformation: Quasi-Quantum Dots Versus Bulk Behavior - Azimi, Seyed Hamed; Kuhri, Susanne; Stahl, Melissa S.; Hou, Yi; Guldi, Dirk Michael; Brabec, Christoph (Advanced Electronic Materials, 2015)
New insights into the complex relation between the thermal phase transformation and the excited state properties of chalcopyrite CuInS nanocrystals (CIS NCs) are presented. An in situ solution processing method via depositing molecular precursors is applied, offering advantages in terms of simplicity, low-temperature processability, and control over crystallite size, and optical properties. At low annealing temperatures, strong carrier quantum confinement and small crystallite sizes are realized for CIS NC films. CIS crystal growth is found to set in at higher annealing temperatures inducing a complete transformation from quasi-quantum-dot (QD) via bulk-like to bulk behavior. The transition of a near-infrared localized surface plasmon resonance (LSPR) towards a bulk-like plasmon resonance documents the crystal growth and further acts as a valuable probe to relate crystallite size with copper-deficient stoichiometries. In addition, time-resolved photophysical investigations help to shed light on the dynamics and mechanisms of exciton and charge carrier generation of CIS NC films as a function of annealing temperature. The in situ-prepared CIS NC films are further passivated by a thin CdS layer, leading to the formation of long-lived excitons and an effective CIS ground-state depletion.
Keywords: chalcopyrite; CuInS2 nanocrystals; exciton generation; localized surface plasmon resonance; transient absorption spectroscopy

Elucidating the Full Potential of OPV Materials Utilizing a High-Throughput Robot-Based Platform and Machine Learning - Du, Xiaoyan; Lüer, Larry; Heumüller, Thomas; Wagner, Jerrit; Berger, Christian; Osterrieder, Tobias; Wortmann, Jonas; Langner, Stefan; Vongsaysy, Uyxing; Bertrand, Melanie; Li, Ning; Stubhan, Tobias; et al. (Joule, 2021)
Evaluating the potential of organic photovoltaic (OPV) materials and devices for industrial production is a multidimensional optimization process with an incredibly large parameter space. Here, we demonstrate automated OPV material and device characterization in terms of efficiency and photostability. Gaussian process regression (GPR) prediction based on optical absorption features guided the optimization process with promising prediction accuracy for PV parameters and burn-in losses. With ∼100 process conditions, screening for efficiency and photostability can be finished within 70 h. The highest power conversion efficiency (PCE) of 14% was achieved by fully automated device fabrication in air with a model material system PM6:Y6. Improving molecular ordering has been identified as the most promising motif for further efficiency optimization. Thin active layers combined with medium thermal annealing temperature are favorable to simultaneously improve efficiency and suppress burn-in losses. The platform and protocol may be expanded to any solution-processed organic semiconductor and interface materials.
CRIS-Team Scopus Importer:2021-02-05
Keywords: automation; efficiency; high-throughput methods; machine learning; organic photovoltaics; photostability; processing optimization

Elucidating the optimal material combinations of organic photovoltaics for maximum industrial viability - Tang, Hua; Liao, Zhihui; Chen, Qianqian; Xu, Han; Huang, Jiaming; Han, Jianhua; Hu, Dingqin; Luo, Ying; Lu, Shirong; Baran, Derya; Li, Gang; Brabec, Christoph; et al. (Joule, 2024)
The choice of donor (D) and acceptor (A) materials in organic solar cells (OSCs) determines the so-called golden triangle of organic photovoltaics (OPV), namely, cost, power conversion efficiency (PCE), and device stability. However, despite the recent advancements in material and device development, determining the optimal material combination for industrialization remains a challenge. Herein, we unveil the optimal material combination that exhibits maximum industrial viability. Specifically, the industrial figure of merit (i-FoM) of seven OPV categories is calculated and further analyzed, including blends of small-molecule donor (SMD):fullerene acceptor, SMD:non-fullerene acceptor (NFA), oligomer donor:NFA, terpolymer:NFA, polymer donor:NFA, polymer donor:polymer acceptor, and single-component materials. Because OPV is approaching wide-scale industrialization, insights into the successes and challenges of these material combinations, particularly their PCE, photostability, and synthetic complexity (SC) index, offer guidance toward accelerating the industrialization of OPV.
CRIS-Team Scopus Importer:2024-08-30
Keywords: industrial viability; material combinations; organic photovoltaics

Embedded Systems and Materials – Research for Advanced Applications, Proceedings of the 1st Chinese-German Summer School in Shanghai - Wellmann, Peter; Shi, Guoyong; Feng, Zhibiao (2006)

Embedding physics domain knowledge into a Bayesian network enables layer-by-layer process innovation for photovoltaics - Ren, Zekun; Oviedo, Felipe; Thway, Maung; Tian, Siyu I. P.; Wang, Yue; Xue, Hansong; Dario Perea, Jose; Layurova, Mariya; Heumüller, Thomas; Birgersson, Erik; Aberle, Armin G.; Brabec, Christoph; et al. (npj Computational Materials, 2020)
Process optimization of photovoltaic devices is a time-intensive, trial-and-error endeavor, which lacks full transparency of the underlying physics and relies on user-imposed constraints that may or may not lead to a global optimum. Herein, we demonstrate that embedding physics domain knowledge into a Bayesian network enables an optimization approach for gallium arsenide (GaAs) solar cells that identifies the root cause(s) of underperformance with layer-by-layer resolution and reveals alternative optimal process windows beyond traditional black-box optimization. Our Bayesian network approach links a key GaAs process variable (growth temperature) to material descriptors (bulk and interface properties, e.g., bulk lifetime, doping, and surface recombination) and device performance parameters (e.g., cell efficiency). For this purpose, we combine a Bayesian inference framework with a neural network surrogate device-physics model that is 100x faster than numerical solvers. With the trained surrogate model and only a small number of experimental samples, our approach reduces significantly the time-consuming intervention and characterization required by the experimentalist. As a demonstration of our method, in only five metal organic chemical vapor depositions, we identify a superior growth temperature profile for the window, bulk, and back surface field layer of a GaAs solar cell, without any secondary measurements, and demonstrate a 6.5% relative AM1.5G efficiency improvement above traditional grid search methods.
CRIS-Team WoS Importer:2020-02-25

Empowering Photovoltaics with Smart Light Management Technologies - Schuster, Christian Stefano; Crupi, Isodiana; Halme, Janne; Koc, Mehmet; Mendes, Manuel João; Peters, Ian Marius; Yerci, Selc¸Uk (Springer International Publishing, 2022)
The daily Sun supplies the continents of the Earth with four times more energy than humanity consumes in a year. This enormous potential of solar energy to generate clean energy is therefore driving great efforts to replace conventional and unsustainable fossil fuel consumption that damages our climate and our environment. Solar photovoltaic (PV) is emerging as the fastest growing renewable energy technology in the world, yet its share to the electricity production currently is less than 3%. While coal and gas remain key to electricity production, the climate crisis demands a fast transition to a carbon-neutral energy system. In the year 2019, the PV industry produced solar panels with a capacity of about 115 GW. To reach multi-TW levels by 2030, PV production capacity needs to scale at high rates, and continued innovation is necessary. One way to increase production is to reduce silicon wafer thickness, making more cells from the amount of silicon produced. Thinning the cell will not only allow making more of them in less time but will also reduce the cost for a module, and for the electricity it generates. A thinner absorber reduces the absorption of sunlight. To counter this loss, optical concepts are needed. In this chapter, we review the most promising approaches in photonics that have made physically thinner but optically thicker solar cells possible. By enabling thinner solar cells, photonic solutions offer the possibility of efficiency enhancements at lower costs. We will explain their applications, discuss their challenges and estimate their impact on energy yield. Finally, we outline how non-silicon thin-film PV is opening up a plethora of consumer-oriented applications. Since the higher flexibility/bendability of thinner cells broadens their applicability range, thin-film PV will empower our transition to a 100% green society in many aspects of our lives.
CRIS-Team Scopus Importer:2024-12-16
Keywords: Dielectric structures; Diffractive structures; Flexible PV; Light-trapping; Photovoltaics; Plasmonics; Solar energy; Tandem solar cells; Thin-film PV

Enabling Ambipolar to Heavy n-Type Transport in PbS Quantum Dot Solids through Doping with Organic Molecules - Nugraha, Mohamad Insan; Kumagai, Shohei; Watanabe, Shun; Sytnyk, Mykhailo; Heiß, Wolfgang; Loi, Maria Antonietta; Takeya, Jun (ACS Applied Materials and Interfaces, 2017)
PbS quantum dots (QDs) are remarkable semiconducting materials, which are compatible with low-cost solution-processed electronic device fabrication. Understanding the doping of these materials is one of the great research interests, as it is a necessary step to improve the device performance as well as to enhance the applicability of this system for diverse optoelectronic applications. Here, we report the efficient doping of the PbS QD films with the use of solution-processable organic molecules. By engineering the energy levels of the donor molecules and the PbS QDs through the use of different cross-linking ligands, we are able to control the characteristics of PbS field-effect transistors (FETs) from ambipolar to strongly n-type. Because the doping promotes trap filling, the charge carrier mobility is improved up to 0.64 cm(-2) V-1 s(-1), which is the highest mobility reported for low-temperature processed PbS FETs employing SiO2 as the gate dielectric. The doping also reduces the contact resistance of the devices, which can also explain the origin of the increased mobility.
Keywords: quantum dots; benzyl viologen; doping; ligands; field-effect transistors

Enabling High Efficiency of Hydrocarbon-Solvent Processed Organic Solar Cells through Balanced Charge Generation and Non-Radiative Loss - Fan, Baobing; Lin, Francis; Oh, Jiyeon; Fu, Huiting; Gao, Wei; Fan, Qunping; Zhu, Zonglong; Li, Wen Jung; Li, Ning; Ying, Lei; Huang, Fei; Yang, Changduk; et al. (Advanced Energy Materials, 2021)
Using non-halogenated solvents to process organic solar cells is preferable because they are less harmful to human health. However, it is challenging to mitigate the delicate trade-offs between solubility and pre-aggregation of organic semiconductors to maintain similar high device efficiencies as those processed by chlorinated solvents. The need for rigorous control of the kinetics between processing temperature and delay time inevitably complicates device processing for achieving reproducible performance. Herein, the authors develop a facile method to achieve proper solubility and pre-aggregation in non-halogenated solvents by selecting suitable donor/acceptor materials and subtle tuning of solvent compositions. This results in films with a high degree of ordering and suitably sized phase separation. Solar cells derived from this process can achieve a high power conversion efficiency up to 18%, which is the highest value reported for non-halogenated solvent processed devices. This impressive result is achieved through synergistically reduced non-radiative loss and enhanced charge generation.
CRIS-Team WoS Importer:2021-10-15

Energy level gamut—a wide-angle lens to look at photoelectronic properties of diketopyrrolopyrrole-benzothiadiazole-based small molecules - Ashtiani Abdi, Ali; Nourmohammadian, Farahnaz; Ameri, Tayebeh (Journal of Molecular Modeling, 2019)
Demands in the field of molecular design for optimized bandgap and proper energy levels to obtain high efficiencies are growing progressively in organic electronics. In the present work, we designed a series of molecules based on diketopyrrolopyrrole (DPP) and benzothiadiazoles (BT). We also studied the efeect of the presence and position of the nitrogen atom as an effective heteroatom. Finally, we optimized the energy levels of the designed structures to find the most favorable donor properties along with fullerene and non-fullerene (NF) acceptors in bulk heterojunction (BHJ) solar cell systems. To shed new light on the electronic characteristics of the designed structures, we developed a correction gamut of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. The gamut is a span that predicts the occurrence of practical HOMO or LUMO with high probability from density functional theory computations in the gas phase. The model was validated using experimental energy level values of a similar structure as reference material. The results obtained by the new pathway of combining the idea of energy level gamuts with the modified Scharber model for NF BHJ suggested that the designed structures can afford power conversion efficiencies (PCE) for NF-BHJ of 8.5–10.5%. [Figure not available: see fulltext.].
CRIS-Team Scopus Importer:2019-07-26
Keywords: Benzothiadiazole; Bulk heterojunction; Diketopyrrolopyrrole; Energy level gamut; Non-fullerene; Organic photovoltaic

Engineering of the Electron Transport Layer/Perovskite Interface in Solar Cells Designed on TiO2 Rutile Nanorods - Shahvaranfard, Fahimeh; Altomare, Marco; Hou, Yi; Hejazi, Seyedsina; Meng, Wei; Osuagwu, Emeka Benedict; Li, Ning; Brabec, Christoph; Schmuki, Patrik (Advanced Functional Materials, 2020)
The engineering of the electron transport layer (ETL)/light absorber interface is explored in perovskite solar cells. Single-crystalline TiO2 nanorod (NR) arrays are used as ETL and methylammonium lead iodide (MAPI) as light absorber. A dual ETL surface modification is investigated, namely by a TiCl4 treatment combined with a subsequent PC61BM monolayer deposition, and the effects on the device photovoltaic performance were evaluated with respect to single modifications. Under optimized conditions, for the combined treatment synergistic effects are observed that lead to remarkable enhancements in cell efficiency, from 14.2% to 19.5%, and to suppression of hysteresis. The devices show J(SC), V-OC, and fill factor as high as 23.2 mA cm(-2), 1.1 V, and 77%, respectively. These results are ascribed to a more efficient charge transfer across the ETL/perovskite interface, which originates from the passivation of defects and trap states at the ETL surface. To the best of our knowledge, this is the highest cell performance ever reported for TiO2 NR-based solar cells fabricated with conventional MAPI light absorber. Perspective wise, this ETL surface functionalization approach combined with more recently developed and better performing light absorbers, such as mixed cation/anion hybrid perovskite materials, is expected to provide further performance enhancements.
Keywords: defect passivation; PC61BM; perovskite solar cells; TiCl4; TiO2 nanorods

Engineering of Wide Bandgap Semiconductor Materials for Energy Saving, Proceedings of the E-MRS 2011 Spring Meeting, Symposium Q - Wellmann, Peter; Syväjärvi, Mikael; Kneissel, Michael (Elsevier, 2012)

Engineering Stable Perovskite Quantum Dot Films for High Color Purity Display Applications - Hu, Huiying; Levchuk, Ievgen; Kalkowski, Felix; Elia, Jack; Osvet, Andres; Brabec, Christoph (ACS Energy Letters, 2023)
Lead halide perovskite nanocrystals (NCs) are the most promising candidates for displays satisfying the Rec. 2020 UHDTV color standard. However, moisture sensitivity currently limits light-emitting applications requiring color stability and purity. In this study, we propose a large-area FAPbBr3-based quantum dot brightness enhancing film (QDEF) strategy developed in our group five years ago. The combination of a polymeric binder tailored to the ligands optimized perovskite NCs for light conversion and demonstrates QDEF applications with 91% coverage of Rec. 2020 standard in tablet displays, using polyhedral oligomeric silsesquioxane-capped FAPbBr3 as the green emitter and K2SiF6: Mn4+ (KSF) as a red emitter. Remarkably, our films operating in displays showed 4 year stability without lead leakage. Even without barrier protection, the unpackaged QDEF maintained 55% of its initial performance. This highlights the importance of a dual stabilization strategy for extending operational and shelf lifetimes of advanced functional perovskite composites.<br

Enhanced dissociation of charge-transfer states in narrow band gap polymer:fullerene solar cells processed with 1,8-octanedithiol - Moet, D. J. D.; Lenes, M.; Morana, M.; Azimi, H.; Brabec, Christoph; Blom, P. W. M. (Applied Physics Letters, 2010)
The improved photovoltaic performance of narrow band gap polymer:fullerene solar cells processed from solutions containing small amounts of 1,8-octanedithiol is analyzed by modeling of the experimental photocurrent. In contrast to devices that are spin coated from pristine chlorobenzene, these cells do not produce a recombination-limited photocurrent. Modeling of the experimental data reveals that a sixfold reduction in the decay rate of photogenerated bound electron-hole pairs can account for the marked increase in short-circuit current density and fill factor. At short-circuit conditions, the dissociation probability of bound pairs is found to increase from 48% to 70%. © 2010 American Institute of Physics.

Enhanced near-infrared response of nano- and microstructured silicon/organic hybrid photodetectors - Derek, Vedran; Glowacki, Eric Daniel; Sytnyk, Mykhailo; Heiß, Wolfgang; Marcius, Marijan; Ristic, Mira; Ivanda, Mile; Sariciftci, Niyazi Serdar (Applied Physics Letters, 2015)
Heterojunctions between an organic semiconductor and silicon are an attractive route to extending the response of silicon photodiodes into the near infrared (NIR) range, up to 2000nm. Silicon-based alternatives are of interest to replace expensive low band-gap materials, like InGaAs, in telecommunications and imaging applications. Herein, we report on the significant enhancement in NIR photodetector performance afforded by nano- and microstructuring of p-doped silicon (p-Si) prior to deposition of a layer of the organic semiconductor Tyrian Purple (TyP). We show how different silicon structuring techniques, namely, electrochemically grown porous Si, metal-assisted chemical etching, and finally micropyramids produced by anisotropic chemical etching (Si μP), are effective in increasing the NIR responsivity of p-Si/TyP heterojunction diodes. In all cases, the structured interfaces were found to give photodiodes with superior characteristics as compared with planar interface devices, providing up to 100-fold improvement in short-circuit photocurrent, corresponding with responsivity values of 1-5mA/W in the range of 1.3-1.6μm. Our measurements show this increased performance is neither correlated to optical effects, i.e., light trapping, nor simply to geometric surface area increase by micro- and nanostructuring. We conclude that the performance enhancement afforded by the structured p-Si/organic diodes is caused by a yet unresolved mechanism, possibly related to electric field enhancement near the sharp tips of the structured substrate. The observed responsivity of these devices places them closer to parity with other, well-established, Si-based NIR detection technologies.
Keywords: Electric fields; Energy gap; Etching; Heterojunctions; Infrared devices; Photodetectors; Photodiodes; Photons; Porous silicon; Semiconductor diodes; Silicon Anisotropic chemical etching; Electric field enhancement; Geometric surface area; Hybrid photo detectors; Metal-assisted chemical etching; Microstructured silicons; Performance enhancements; Short-circuit photocurrent; Semiconducting silicon

Enhanced Photostability of Lead Halide Perovskite Nanocrystals with Mn3+ Incorporation - Hu, Huiying; Fehn, Dominik; Barr, Maissa; Harreiß, Christina; Zhao, Yicheng; Meyer, Karsten; Osvet, Andres; Brabec, Christoph (ACS Applied Materials and Interfaces, 2024)
Recently, lead halide perovskite nanocrystals (NCs) have shown great potential and have been widely studied in lighting and optoelectronic fields. However, the long-term stability of perovskite NCs under irradiation is an important challenge for their application in practice. Mn2+ dopants are mostly proposed as substitutes for the Pb site in perovskite NCs synthesized through the hot-injection method, with the aim of improving both photo- and thermal stability. In this work, we employed a facile ligand-assisted reprecipitate strategy to introduce Mn ions into perovskite lattice, and the results showed that Mn3+ instead of Mn2+, even with a very low level of incorporation of 0.18 mol % as interstitial dopant, can enhance the photostability of perovskite binder film under the ambient conditions without emission change, and the photoluminescent efficiency can retain 70% and be stable under intensive irradiation for 12 h. Besides, Mn3+ incorporation could prolong the photoluminescent decay time by passivating trap defects and modifying the distortion of the lattice, which underscores the significant potential for application as light emitters.
CRIS-Team Scopus Importer:2024-05-17
Keywords: interstitial doping; passivation; perovskite nanocrystal; photoluminescence; photostability

Enhanced photosynthetic activity in Spinacia oleracea by spectral modification with a photoluminescent light converting material - Xia, Qi; Batentschuk, Miroslaw; Osvet, Andres; Richter, Peter; Häder, Donat-Peter; Schneider, Juergen; Brabec, Christoph; Wondraczek, Lothar; Winnacker, Albrecht (Optics Express, 2013)
The spectral conversion of incident sunlight by appropriate photoluminescent materials has been a widely studied issue for improving the efficiency of photovoltaic solar energy harvesting. By using phosphors with suitable excitation/emission properties, also the light conditions for plants can be adjusted to match the absorption spectra of chlorophyll dyes, in this way increasing the photosynthetic activity of the plant. Here, we report on the application of this principle to a high plant, Spinacia oleracea. We employ a calcium strontium sulfide phosphor doped with divalent europium (Ca0.4Sr0.6S:Eu2+, CSSE) on a backlight conversion foil in photosynthesis experiments. We show that this phosphor can be used to effectively convert green to red light, centering at a wavelength of 650 nm which overlaps the absorption peaks of chlorophyll a/b pigments. A measurement system was developed to monitor the photosynthetic activity, expressed as the CO2 assimilation rate of spinach leaves under various controlled light conditions. Results show that under identical external light supply which is rich in green photons, the CO2 assimilation rate can be enhanced by more than 25% when the actinic light is modified by the CSSE conversion foil as compared to a purely reflecting reference foil. These results show that the phosphor could be potentially applied to modify the solar spectrum by converting the green photons into photosynthetically active red photons for improved photosynthetic activity. © 2013 Optical Society of Americ
Keywords: Engineering controlled terms: Carbon dioxide; Light emission; Phosphors; Photons; Plants (botany); Solar energy; Calcium Assimilation rate; Measurement system; Photoluminescent materials; Photosynthetic activity; Photovoltaic solar energy; Spectral conversion; Spectral modifications; Strontium sulfide phosphor; Divalent europium Engineering main heading: Light EMTREE drug terms: carbon dioxide; strontium EMTREE medical terms: article; chemistry; luminescence; metabolism; photon; photosynthesis; physiology; spectrofluorometry; spinach; time MeSH: Carbon Dioxide; Luminescence; Photons; Photosynthesis; Spectrometry; Fluorescence; Spinacia oleracea; Strontium; Time Factors Medline is the source for the MeSH terms of this document.

Enhancement of accuracy of neutron atomic resolution holography - Kanazawa, Y.; Fukumoto, Youhei; Uechi, Shiyouichi; Ohoyama, Kenji; Lederer, Maximilian; Happo, Naohisa; Hayashi, Koichi; Harada, Masahide; Tsutsui, Kazuo (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2018)
CRIS-Team WoS Importer:2019-07-19

Enhancement of the Power Conversion Efficiency in Organic Photovoltaics by Unveiling the Appropriate Polymer Backbone Enlargement Approach - Chochos, Christos L.; Singh, Ranbir; Kim, Min; Gasparini, Nicola; Katsouras, Athanasios; Kulshreshtha, Chandramouli; Gregoriou, Vasilis G.; Keivanidis, Panagiotis E.; Ameri, Tayebeh; Brabec, Christoph; Cho, Kilwon; Avgeropoulos, Apostolos (Advanced Functional Materials, 2016)
Optoelectronic properties, supramolecular assemblies, and morphology variation of polymeric semiconductors are governed by six fundamental chemical features. These features are molecular weight, bond length alternation (BLA), planarity, aromatic resonance energy, substituents, and intermolecular interactions. Of these features the specific role of BLA in determining the performance of a polymeric semiconductor in practical technological applications is so far unknown. This study investigates this question and reports the novel finding that the optoelectronic, microscopic (supramolecular packing), and macroscopic (morphology variation and device performance) properties of model semiconducting polymers depend on the conjugated polymer backbone enlargement, which is directly related to the BLA. Extensive studies are performed in both single-component polymer films and their blends with fullerene derivatives. Understanding the specific structure-properties relations will lead to significant advancement in the area of organic electronics, since it will set new design rules toward further optimization of polymer chemical structures to enhance the device performances. An efficient way to enlarge the polymer backbone of an electron donor conjugated polymer toward higher organic photovoltaic performance is presented.
Keywords: morphology; organic electronics; polymer semiconductors; recombination dynamics; supramolecular assembly

Enhancement of up-conversion luminescence in Er,Ce doped Y3-xYbxAG single crystalline films - Zorenko, Yu.; Gorbenko, V.; Zorenko, T.; Paprocki, Kazimierz; Osvet, Andres; Batentschuk, Miroslaw; Brabec, Christoph; Fedorov, A. (Journal of Luminescence, 2016)
The paper deals with investigation of the luminescent properties of Er and Er/Ce doped solid solutions of YYbAG garnets with x values ranging from 0 to 3.0, prepared by the LPE method in the form of single crystalline films (SCF). We have found that the effective Ce→Yb energy transfer is observed in the YYbAlO:Er,Ce garnets (YYbAG:Er,Ce). Apart from that, strong enhancement of the Er upconvesion luminescence in YYbAG:Er,Ce garnets was found due to the Ce codoping. Among all the investigated samples of solid solutions of mixed YYbAG:Er,Ce garnets, the highest intensity of the up-conversion luminescence is observed for the YYbAG:Er,Ce SCF.
Keywords: Er and Ce dopant; Liquid phase luminescence; Mixed Y3-xYbxAG garnet; Single crystalline films; Up conversion luminescence

Enhancing deep visible-light photoelectrocatalysis with a single solid-state synthesis: Carbon nitride/TiO2 heterointerface - Silva, Ingrid F.; Pulignani, Carolina; Odutola, Jokotadeola; Galushchinskiy, Alexey; Texeira, Ivo F.; Isaacs, Mark; Mesa, Camilo A.; Scoppola, Ernesto; These, Albert; Badamdorj, Bolortuya; Ángel Muñoz-Márquez, Miguel; Zizak, Ivo; et al. (Journal of Colloid and Interface Science, 2025)
Visible-light responsive, stable, and abundant absorbers are required for the rapid integration of green, clean, and renewable technologies in a circular economy. Photoactive solid–solid heterojunctions enable multiple charge pathways, inhibiting recombination through efficient charge transfer across the interface. This study spotlights the physico-chemical synergy between titanium dioxide (TiO2) anatase and carbon nitride (CN) to form a hybrid material. The CN(10%)-TiO2(90%) hybrid outperforms TiO2 and CN references and literature homologs in four photo and photoelectrocatalytic reactions. CN-TiO2 achieved a four-fold increase in benzylamine conversion, with photooxidation conversion rates of 51, 97, and 100 % at 625, 535, and 465 nm, respectively. The associated energy transfer mechanism was elucidated. In photoelectrochemistry, CN-TiO2 exhibited 23 % photoactivity of the full-spectrum measurement when using a 410 nm filter. Our findings demonstrate that CN-TiO2 displayed a band gap of 2.9 eV, evidencing TiO2 photosensitization attributed to enhanced charge transfer at the heterointerface boundaries via staggered heterojunction type II.
CRIS-Team Scopus Importer:2024-09-20
Keywords: Benzylamine photooxidation; CN-TiO; Heterointerface; Hydrogen production; TiO

Enhancing Planar Inverted Perovskite Solar Cells with Innovative Dumbbell-Shaped HTMs: A Study of Hexabenzocoronene and Pyrene-BODIPY-Triarylamine Derivatives - Rocha-Ortiz, Juan S.; Wu, Jianchang; Wenzel, Jonas; Bornschlegl, Andreas; Perea, Jose Dario; Leon, Salvador; Barabash, Anastasia; Wollny, Anna-Sophie; Guldi, Dirk Michael; Zhang, Jiyun; Insuasty, Alberto; Lüer, Larry; et al. (Advanced Functional Materials, 2023)
Keywords: hexabenzocoronene; donor–acceptor; BODIPY; π-conjugation; perovskite solar cells; hole-transport materials

Entwicklung einer katalytisch funktionalen porösen Keramik auf Basis hydraulisch aktiver Oxid-Keramiken - Enderle, Ralph; Göbbels, Matthias; Götz-Neunhoeffer, Friedlinde (European Journal of Mineralogy, 2003)
UnivIS-Import:2015-03-09:Pub.2003.nat.dgeo.IGM.LM.entwic

Entwicklung einer porösen Calciumphosphat-Keramik im Hinblick auf die Verwendung als Knochenersatzstoff - Göbbels, Matthias; Enderle, Ralph; Götz-Neunhoeffer, Friedlinde (European Journal of Mineralogy, 2005)
UnivIS-Import:2015-03-09:Pub.2005.nat.dgeo.IGM.LM.entwic

Environmentally Printing Efficient Organic Tandem Solar Cells with High Fill Factors: A Guideline Towards 20% Power Conversion Efficiency - Li, Ning; Baran, Derya; Spyropoulos, George D.; Zhang, Hong; Berny, Stephane; Turbiez, Mathieu; Ameri, Tayebeh; Krebs, Frederik C.; Brabec, Christoph (Advanced Energy Materials, 2014)
The tandem concept involves stacking two or more cells with complementary absorption spectra in series or parallel connection, harvesting photons at the highest possible potential. It is strongly suggested that the roll-to-roll production of organic solar cells will employ the tandem concept to enhance the power conversion efficiency (PCE). However, due to the undeveloped deposition techniques, the challenges in ink formulation as well as the lack of commercially available high performance active materials, roll-to-roll fabrication of highly efficient organic tandem solar cells currently presents a major challenge. The reported high PCE values from lab-scale spin-coated devices are, of course, representative, but not helpful for commercialization. Here, organic tandem solar cells with exceptionally high fill factors and PCE values of 7.66% (on glass) and 5.56% (on flexible substrate), which are the highest values for the solution-processed tandem solar cells fabricated by a mass-production compatible coating technique under ambient conditions, are demonstrated. To predict the highest possible performance of tandem solar cells, optical simulation based on experimentally feasible values is performed. A maximum PCE of 21% is theoretically achievable for an organic tandem solar cell based on the optimized bandgaps and achieved fill factors.
Keywords: flexible electronics; large-scale production; organic photovoltaics; organic solar cells; solution processing

Environmentally safe layered crystal produced from hazardous chemical elements: TlPb2BrI4, a new promising detector material - Khyzhun, O. Y.; Vu, Tuan V.; Parasyuk, O. V.; Fedorchuk, A. O.; Fochuk, P. M.; Lavrentyev, A. A.; Gabrelian, B. V.; Levchuk, Ievgen; Matt, Gebhard; Tedde, Sandro F.; Schmidt, Oliver; Shrestha, Shreetu; et al. (Journal of Alloys and Compounds, 2022)
Exploring better Gamma, X-Ray and IR-Mid-R detectors, adequately sensitive to ambient temperatures and environmental conditions, is highly desirable. Therefore, following this path, we present detecting opportunities, based on data of experimental and theoretical investigation of the electronic and optical properties, photocurrent behavior at different bias voltages as well as the reflection for the He-Cd cw laser after irradiation by three different IR laser wavelengths, for recently grown TlPb2BrI4 single crystal with strong anisotropic, two-dimensional (2D) layered structure. The X-ray photoelectron spectroscopy brings data on binding energy values of core levels of TlPb2BrI4 for both as-grown and Ar+-ion-treated crystal surfaces as well as for elucidation of the energy distribution of the valence electronic states. In opposite to well-known IR-detector materials, TlPb2BrI4 crystal surface shows high chemical stability concerning Ar+-ion bombardment. Further, we carry out ab initio band-structure calculations to gain curves of total and partial densities of states and to elucidate the principal optical constants of TlPb2BrI4. The present studies indicate that, in spite of the fact that the TlPb2BrI4 crystal contains two very hazardous/toxic chemical elements, thallium and lead; however, it is chemically stable and reveals very low hygroscopic behavior when being exposed to environmental conditions.
CRIS-Team Scopus Importer:2022-09-02
Keywords: Electronic structure; First-principal computation; Lead; Hazardous elements; Thallium; XPS

Epitaxial growth of single crystalline film phosphors based on the Ce3+-doped Ca2YMgScSi3O12 garnet - Gorbenko, V.; Zorenko, T.; Paprocki, Kazimierz; Iskatiyeva, A.; Fedorov, A.; Schroeppel, F.; Levchuk, Ievgen; Osvet, Andres; Batentschuk, Miroslaw; Zorenko, Yu (Crystengcomm, 2017)
In this work, we present for the first time the results on crystallization and investigation of the luminescence properties of new prospective phosphors based on single crystalline films (SCFs) of Ce3+-doped Ca2YMgScSi3O12 silicate garnet, grown by the liquid phase epitaxy (LPE) method onto Y3Al5O12 (YAG) substrates. The luminescence properties of Ca2YMgScSi3O12:Ce SCFs were compared with the properties of the reference YAG:Ce SCF sample. The influence of thermal annealing at 1000–1300 °C in a N2/H2 reducing atmosphere on the optical properties of Ca2YMgScSi3O12 SCFs was investigated as well. The results of this research can be suitable for the development of a new generation of white LED converters and scintillators based on the epitaxial structures of Ca2+–Si4+ containing garnets, grown by the LPE method onto undoped or doped substrates of garnet compounds.<br

Epitaxial Metal Halide Perovskites by Inkjet-Printing on Various Substrates - Sytnyk, Mykhailo; Yousefi-Amin, Amir Abbas; Freund, Tim; Prihoda, Annemarie; Götz, Klaus; Unruh, Tobias; Harreiß, Christina; Will, Johannes; Spiecker, Erdmann; Levchuk, Jevgen; Osvet, Andres; Brabec, Christoph; et al. (Advanced Functional Materials, 2020)
Metal-halide-perovskites revolutionized the field of thin-film semiconductor technology, due to their favorable optoelectronic properties and facile solution processing. Further improvements of perovskite thin-film devices require structural coherence on the atomic scale. Such perfection is achieved by epitaxial growth, a method that is based on the use of high-end deposition chambers. Here epitaxial growth is enabled via a approximate to 1000 times cheaper device, a single nozzle inkjet printer. By printing, single-crystal micro- and nanostructure arrays and crystalline coherent thin films are obtained on selected substrates. The hetero-epitaxial structures of methylammonium PbBr(3)grown on lattice matching substrates exhibit similar luminescence as bulk single crystals, but the crystals phase transitions are shifted to lower temperatures, indicating a structural stabilization due to interfacial lattice anchoring by the substrates. Thus, the inkjet-printing of metal-halide perovskites provides improved material characteristics in a highly economical way, as a future cheap competitor to the high-end semiconductor growth technologies.
CRIS-Team Scopus Importer:2020-09-11
Keywords: epitaxial growth; inkjet printing; metal-halide-perovskites; single-crystal-microstructures

Erratum: A multi-objective optimization-based layer-by-layer blade-coating approach for organic solar cells: Rational control of vertical stratification for high performance (Energy and Environmental Science (2019) 12 (3118-3132) DOI: 10.1039/C9EE02295C) - Sun, Rui; Guo, Jie; Wu, Qiang; Zhang, Zhuohan; Yang, Wenyan; Guo, Jing; Shi, Mumin; Zhang, Yaohong; Kahmann, Simon; Ye, Long; Jiao, Xuechen; Loi, Maria A.; et al. (Energy and Environmental Science, 2020)
The Acknowledgements section should have included the following sentence: "This work was performed in part on the SAXS/ WAXS beamline at the Australian Synchrotron, part of ANSTO". The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.
CRIS-Team Scopus Importer:2020-02-04

Erratum: In(iii)-dictated formation of double Cs2AgxNa1−xFeyIn1−yCl6 perovskites (J. Mater. Chem. C (2023) 11 (6867–6873) DOI: 10.1039/D3TC01138) - Stroyuk, Oleksandr; Raievska, Oleksandra; Barabash, Anastasia; Hauch, Jens; Brabec, Christoph (Journal of Materials Chemistry C, 2023)
The authors regret errors in Fig. 1(d) of the published article, in which the XRD patterns in Fig. 1(d) were incorrectly labelled with the In fraction values instead of the Fe fraction y values; in addition, the curves should have been numbered to correspond with the discussion in the main text. The corrected Fig. 1 image and caption are as shown here. (Figure Presented). The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.
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Erratum to “Optimization of KOH etching parameters for quantitative defect recognition in n- and p-type doped SiC”: [J. Crystal Growth 289 (2006) 520–526] - Sakwe, Aloysius; Müller, Robin; Wellmann, Peter (Journal of Crystal Growth, 2007)